JP2008232142A - Cooled egr system and heat exchanger for system thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooled EGR system capable of improving the thermal efficiency of an engine and a heat exchanger for the cooled EGR system capable of providing excellent heat exchange performance. <P>SOLUTION: In the EGR system taking part of exhaust gas out of an exhaust system as EGR gas, cooling the same by an EGR cooling device, and returning the same to an intake system of the engine again, the EGR gas cooling device is constructed to be cooled by cooling air introduced from an intercooler or cooling air supplied from an outside, and the cooling air is forcibly circulated by a compressor, a fan or a blower provided in an flow-in side of the EGR gas cooling device. A multiple pipe type heat exchanger or the like having a plurality of flat heat conduction pipe in a shell main body having a rectangular section shape with keeping intervals is used in the EGR gas cooling device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cooled EGR system in which a part of the exhaust gas is taken out from the exhaust system as EGR gas and returned to the engine intake system and circulated, and a multi-tube heat exchanger (EGR gas) used in the cooled EGR system. Cooling device).

  In the EGR system, combustion air is introduced into the intake system of the engine via an intercooler, and a part of the exhaust gas of the engine is taken out from the exhaust system and returned to the intake system of the engine again through the EGR gas cooling device. As the EGR gas cooling device used in this system, a heat transfer tube group is fixedly arranged on a tube sheet fixed near both ends of the inner wall of the trunk tube, and outside the both ends of the trunk tube. A multi-tubular structure in which an EGR gas inlet and outlet are provided on the fixed end cap is generally used. In this multi-tube type, a number of gas-liquid heat exchange type EGR gas cooling devices that cool the gas EGR gas with engine cooling water have been proposed.

  As this gas-liquid heat exchange type EGR gas cooling device, for example, in a heat exchanger in which an outer pipe for passing a liquid is disposed outside an inner pipe for passing a high-temperature EGR gas, and heat is exchanged between the gas and the liquid. A double-pipe heat exchanger (for example, refer to Patent Document 1) in which a corrugated fin made of a metallic thin plate is internally provided in the inner pipe, an inner pipe for allowing a medium to be cooled to flow inside, and the inner pipe A double tube heat exchanger (see, for example, Patent Document 2) comprising an outer tube provided so as to surround the outer periphery and a heat dissipating fin disposed inside the inner tube and having a thermal stress relaxation function. ) Etc. are known.

Many of the double-pipe heat exchangers equipped with the fin structure as described above have already been put to practical use as heat exchangers for cooling the EGR gas, but are fluids that flow because they are compact in structure. As a result, there is an unresolved problem in the total heat exchange efficiency. In order to solve such a problem, even if the structure is somewhat complicated and the size must be increased, so-called shell and tube type multi-tubular heat exchangers must be employed. Improvements have been made.
As an example of a shell-and-tube type multi-tube heat exchanger, a nozzle serving as a cooling water inlet and a cooling water outlet at one end of the outer peripheral portion of the shell main body constituting the cooling jacket are respectively attached to the shell. A hood for introducing high-temperature EGR gas is provided at one end in the longitudinal direction of the main body, and a hood for discharging EGR gas after heat exchange is provided integrally at the other end, and a tube sheet attached to the inside of each bonnet is provided. A plurality of flat heat transfer tubes are attached at intervals, and hot EGR gas flows through the flat heat transfer tubes so as to intersect with the cooling water flowing through the shell body, and In addition to a wide heat transfer area formed by a plurality of flat heat transfer tubes, a plate fin having a U-shaped channel shape is provided on the inner peripheral surface of the flat heat transfer tubes. By doing so, the flow of the EGR gas flowing through is trickled, and at the same time, the heat transfer area is further increased, and the heat exchange efficiency is excellent (for example, patent document) 3) is disclosed.

Recently, as an example of another heat exchange type cooling device including the EGR gas cooling device, a shell and tube type multi-tube heat exchanger 200 as shown in FIG. 14 is not limited to the EGR gas cooling device. A plurality of heat transfer tube groups 203 are formed through a tube sheet 205 in a shell 201 that is widely adopted and through which cooling water flows, and a high temperature introduced from a cooling medium inlet g1 provided in the bonnet 202-1. Until the fluid is discharged from the cooled medium outlet g2 provided on the opposite bonnet 202-2, the inside of the shell 201 is passed through the tube wall of the heat transfer tube forming the heat transfer tube group 203. Heat is exchanged with cooling water that flows in a state orthogonal to the flow of the medium to be cooled, and is cooled to a predetermined temperature. Further, by making the individual heat transfer tubes 203-1 forming the heat transfer tube group 203 into flat tubes as shown in FIGS. 15 (a) and (b), the contact area can be increased, A corrugated plate fin 206 having a rectangular cross section in the heat pipe 203-1 and having a free shape in the longitudinal direction is provided, and the flow path of the high-temperature fluid that is the cooling medium is divided into a plurality of small flow paths, The plate fin 206 is formed in a waveform as shown in FIG. 5C, and the fluid flowing through the small flow path is meandered, thereby reducing the flow velocity and further increasing the heat transfer area, A fin structure has been proposed for further improving the heat exchange efficiency.
Japanese Patent Laid-Open No. 11-23181 JP 2000-1111277 A JP 2002-107091 A

  However, the heat transfer area is expanded by arranging a plurality of flat heat transfer tubes, and a special plastic working is applied to the plate material made of a single metal thin plate in the flat heat transfer tubes. Also in the multi-tube heat exchanger with the fin structure incorporated therein, the pressure loss of the fluid in the small flow path formed by the fin structure is low, and the distribution of the fluid flowing between the small flow paths However, the above small flow paths divided by plate fins formed by a single sheet of metal form an independent flow path to each other. It is impossible to eliminate the non-uniformity of the flow velocity distribution once generated, and there remains an unsolved problem that the heat exchange efficiency is reduced due to the uneven flow velocity distribution. . On the other hand, in the conventional multi-tube heat exchanger, a flat heat transfer tube through which the medium to be cooled flows is provided with a fin structure so that a stirring effect is generated in the fluid flow. However, the flow of cooling water, which is the cooling medium that flows outside the flat heat transfer tubes, is only considered to flow sequentially in a specific direction by the baffle, and in order to improve heat transfer performance In reality, the air-to-air heat exchange type heat exchanger adopting air as a cooling medium has not yet achieved sufficient performance.

Moreover, since the EGR gas cooling device (EGR cooler) in the conventional water-cooled cooled EGR system cools the gas EGR gas with the engine cooling water as described above, the thermal energy of the cooled EGR gas is the EGR cooler. Once transmitted to the engine coolant, it is then dissipated from the radiator. For this reason, components and parts of the cooling system such as a radiator, a cooling fan, and a water pump are increased in size, and the amount of the engine cooling water is increased as compared with the conventional engine, so that the weight is inevitably increased as a whole.
On the other hand, in recent years, from the viewpoint of preventing global warming, there has been a further demand for a reduction in CO ₂ emissions from vehicles equipped with engines, and there is a desire for smaller and lighter engines and lighter vehicles. However, the fact that the EGR cooler that reduces NOx and does not deteriorate fuel consumption is a water-cooled type that causes an increase in weight is not preferable in terms of an increase in the weight of the engine and the vehicle, and an improvement has been desired.

  The present invention has been made in view of the above-described actual situation, and compared with the case of only a cooled EGR system capable of further improving the thermal efficiency of an engine and a conventional water-cooled EGR cooler, the devices constituting the cooling system. In addition, it is an object of the present invention to propose a heat exchanger for a cooled EGR system that can contribute to the prevention of global warming as well as being able to reduce the size and weight of parts and obtain excellent heat exchange performance.

  The cooled EGR system according to the present invention is an EGR system in which a part of exhaust gas is taken out from the exhaust system as EGR gas, cooled by the EGR gas cooling device, and returned to the intake system of the engine again. It is cooled by the cooling air introduced from the outside or the cooling air supplied from the outside. The cooling air in the EGR system is preferably forced to flow by a compressor, a fan, or a blower provided on the inflow side of the EGR gas cooling device. Further, it is preferable that a water-cooled EGR gas cooling device is incorporated upstream or downstream of the air-cooled EGR gas cooling device. Further, in the EGR system of the present invention, it is preferable to employ a multi-tube heat exchanger for the air-cooled EGR gas cooling device, and the multi-tube heat exchanger is the air-cooled EGR gas cooling device. However, it is more preferable that the heat exchanger is a multi-tube heat exchanger in which a plurality of flat heat transfer tubes are arranged at intervals in a shell body having a rectangular cross-sectional shape.

  The multi-tube heat exchanger for an EGR system according to the present invention is a multi-tube heat exchanger in which a plurality of flat heat transfer tubes are arranged at intervals in a shell body having a rectangular cross section. A coil spring formed by spirally winding a wire rod in a space formed between the outer peripheral surface of the flat heat transfer tube adjacent to the inner peripheral surface of the body and a space generated between the outer peripheral surfaces of the adjacent flat tubes; At least one fin structure made of a flat coil spring having a flat cross section formed by winding a wire rod in a flat shape is disposed, and the fin structure made of the coil spring or the flat coil spring is arranged at a predetermined interval. The flat heat transfer tube outer peripheral surface adjacent to the shell main body inner peripheral surface and / or the adjacent flat heat transfer tube outer peripheral surface are closely attached and fixed to each other. . In this multitubular heat exchanger, it is preferable that the inner peripheral surface of the flat heat transfer tube is preliminarily provided with a corrugated fin having a cross-sectional channel shape or a fin structure made of the flat coil spring, and the coil spring or The fin structure composed of the flat coil springs is formed in a space formed between the inner peripheral surface of the shell body and the outer peripheral surface of the adjacent flat heat transfer tube, and in a space generated between the outer peripheral surfaces of the adjacent flat heat transfer tubes. It is preferable that the heat transfer tube is closely attached and fixed in any form of parallel, corrugated, vertical, and oblique directions with respect to the tube axis direction of the heat transfer tube, or an arbitrary combination thereof.

  The fixing means for the fin structure comprising the coil spring or the flat coil spring in the multi-tube heat exchanger according to the present invention to the inner peripheral surface of the shell body and / or the outer peripheral surface of the flat heat transfer tube may be welding, brazing, or the like. Appropriately selected from among attachment, diffusion and other joining means.

  In the multi-tube heat exchanger according to the present invention, the coil spring or the flat coil spring forming the fin structure is made of a metal wire, and a pitch interval generated between the wires is maintained at 2 to 10 mm. The winding cross-sectional shape is any one of a flattened substantially oval shape, a substantially oval shape, a substantially rectangular shape, and a substantially hexagonal shape.

  Further, in the multi-tube heat exchanger according to the present invention, the cross section of the metal wire forming the coil spring or the flat coil spring is circular or substantially oval or substantially oval deformed arbitrarily based on the circle. , A triangular shape, a substantially rectangular shape, a substantially pentagonal shape, a substantially hexagonal shape, a substantially polygonal shape, or a star shape arbitrarily deformed based on the square.

  Still further, in the multitubular heat exchanger according to the present invention, the metal wire forming the coil spring or the flat coil spring is made of stainless steel, aluminum, copper, iron, titanium, nickel and alloys based on these, It is preferable that these metals are subjected to surface treatment such as plating or thermal spraying as desired.

  In the multi-tube heat exchanger according to the present invention, the coil spring or the flat coil spring is disposed in a flow path formed in a space between the inner peripheral surface of the shell body and the outer peripheral surface of the flat heat transfer tube, and the flow path The cooling medium flows through the flow path formed on the inner peripheral surface of the flat heat transfer tube, the cooling medium is cooling air, and the cooling medium is exhaust gas. is there.

The cooled EGR system according to the present invention is a system in which an EGR gas cooling device cools with cooling air introduced from the intercooler or cooling air supplied from the outside, and the cooling air is supplied to the EGR gas cooling device. By adopting a multi-tube heat exchanger that is forced to flow by a compressor or fan or blower provided on the inflow side and that has excellent heat exchange performance in an EGR gas cooling device (EGR cooler), The excellent effect of exhibiting excellent temperature efficiency and further improving the thermal efficiency of the engine can be obtained.
That is, according to the cooled EGR system of the present invention, the high-temperature exhaust gas discharged from the engine room is introduced into the multi-tubular heat exchanger constituting the EGR cooler and cooled by the intercooler or from the outside. Since the introduced cooling air is forcibly introduced by a compressor, a fan or a blower, it is efficiently cooled and circulated to the intake system of the engine, so that the thermal efficiency of the engine is further improved.
When an EGR gas cooling system is configured by arranging an air cooling system and a water cooling system in series as an EGR gas cooling device (EGR cooler) in series, when using an air cooling EGR gas cooling device for the precooler, When the EGR gas inlet near the EGR gas inlet does not cause a boiling phenomenon from the outer surface of the heat transfer tube, the amount of heat transfer does not decrease. On the other hand, when an air-cooled EGR gas cooling device is used for the aftercooler, Such condensation on the inner surface of the heat transfer tube due to supercooling in the vicinity of the EGR gas outlet does not cause deterioration due to corrosion of the heat transfer tube and engine parts.

  On the other hand, the multitubular heat exchanger according to the present invention is formed between the space formed between the inner peripheral surface of the shell body and the outer peripheral surface of the adjacent flat heat transfer tube, and the adjacent flat heat transfer tube outer peripheral surface. A fin structure comprising a coil spring formed by winding a metal wire in a spiral shape and a coil spring having a flat wound cross-sectional shape is disposed in the space, and further in the flat heat transfer tube In the case of a corrugated fin made of a thin metal plate having a cross-sectional channel shape and corrugated in the longitudinal direction, or the coil spring or the flat coil spring, and a flat heat transfer tube with the corrugated fin, the flow divided into small channels Since the fluid flowing through the channel can flow between each channel, the balance between the flow rate and the flow rate between each channel is maintained almost uniformly. A high-temperature exhaust gas, which is a medium to be cooled, flows through the fluid flow path formed on the inner peripheral surface of the flat heat transfer tube, and the fluid flow path formed between the outer peripheral surface of the flat heat transfer tube and the inner peripheral surface of the shell body is the cooling medium. As air flows, so-called gas-gas heat exchange is performed across the tube wall of the flat heat transfer tube. At this time, the high-temperature exhaust gas flowing through the flat heat transfer tube has a built-in waveform. The corrugated fins agitate the flow appropriately, and the flow velocity of the fluid is not biased, and the non-uniform flow velocity distribution is eliminated, and the fluid pressure is uniform between the flow paths. Uniformity is achieved, fluid distribution is averaged, and the effect of ensuring excellent heat exchange performance is obtained. In the case of the flat heat transfer tube with the coil spring or the flat coil spring, the coil Spring or bias Since the coil spring is interposed in the flow path of the fluid to be cooled or flowing through the flat heat transfer tube, a large number of edge portions are present intermittently and without interruption. In addition, a Karman vortex street is continuously formed for each wire formed in a spiral shape, and the flow velocity of the fluid in the heat transfer tube is not biased with a large stirring effect. Uniform flow velocity distribution is eliminated and it is easy to maintain the uniform flow velocity. As above, the fluid pressure is uniform between each flow path, the fluid distribution is averaged, and the heat transfer performance is dramatically improved. Improved to ensure excellent heat exchange performance.

  Furthermore, by a fin structure composed of a spiral coil spring or a flat coil spring that is disposed and fixed in advance in a fluid flow path composed of air that is a cooling medium formed on the outer peripheral surface of the flat heat transfer tube, Mixing and collisions between fluids that flow frequently occur, turbulence and vortexing of the working fluid occur, and its streamline is disturbed in a complex manner, and many edges are intermittent and uninterrupted Due to the existence, the edge effect on the flowing fluid is continuously produced, the laminar flow is peeled away and heat exchange through the heat transfer tube wall is efficiently promoted, and the air-air heat exchange type In spite of the multitubular heat exchanger, excellent cooling efficiency is effectively ensured.

The multi-tube heat exchanger according to the present invention is disposed and fixed between the inner peripheral wall surface of the shell body and the adjacent flat heat transfer tube outer peripheral wall surface, and between the adjacent flat heat transfer tube outer peripheral wall surfaces. The fin structure composed of the coil spring and the flat coil spring acts as a support in each space, so that the reinforcing effect is added, and the rigidity such as vibration resistance is improved, and the fixing means for the fin structure By selecting brazing, welding, or diffusion bonding and fixing them evenly, heat transfer through the heat transfer tube wall surface through metal wire is further improved, and excellent heat exchange efficiency is ensured. be able to. Therefore, the air-air heat exchange type multi-tubular heat exchanger of the present invention can be easily incorporated into a cooled EGR system, and its excellent heat exchange performance enables the reduction of the size and weight of these devices. Therefore, it can be easily installed in a limited space, so that it can be provided as an EGR gas cooling system with outstanding layout. Furthermore, the cooled EGR system employing the air-to-air heat exchange type multi-tube heat exchanger of the present invention is a component constituting the cooling system as compared to the conventional cooled EGR system employing only the water-cooled EGR cooler. As a result, the heat exchange performance and the excellent heat exchange performance can be obtained, which can greatly contribute to the prevention of global warming.
Needless to say, the multi-tube heat exchanger of the present invention is not limited to the air-cooled EGR cooler in the cooled EGR system, and can be used for a wide range of applications such as an exhaust gas heat exchanger.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings and examples. However, the present invention is not restricted thereby, and design changes can be freely made within the scope of the gist of the present invention. Is possible.

  FIG. 1 is a schematic diagram showing a first embodiment of a cooled EGR system according to the present invention, FIG. 2 is a schematic diagram showing a second embodiment of the cooled EGR system, and FIG. 3 is a third embodiment of the cooled EGR system. FIG. 4 is a schematic view showing a fourth embodiment of the cooled EGR system, FIG. 5 is a schematic longitudinal front view showing an embodiment of the multi-tube heat exchanger according to the present invention, and FIG. FIG. 7 is a schematic perspective view showing a part of a flat heat transfer tube incorporated in the multi-tube heat exchanger, and FIG. 8 is a flat heat transfer tube same as the above. 9 is a schematic perspective view showing a corrugated fin corrugated in advance, FIG. 9 is a schematic longitudinal sectional front view showing a part of another embodiment of the multi-tube heat exchanger according to the present invention, and FIG. In the schematic diagram which shows the simple substance of the flat heat exchanger tube incorporated in the multi-tube heat exchanger shown, FIG. 11A is a partially omitted perspective view of a flat heat transfer tube having a flat coil spring incorporated therein, FIG. 11B is a partially omitted perspective view of a flat coil spring alone, and FIG. 11 is a winding of a fin structure comprising a coil spring according to the present invention. FIGS. 12A and 12E are front views illustrating a state in which the winding cross-sectional shape is formed flat, and FIG. 12 is a diagram of a metal wire forming a coil spring that becomes the fin structure of the above. FIGS. 13A and 13H are cross-sectional views illustrating the cross-sectional shape, and FIG. 13 illustrates a flat heat transfer tube disposed in a multi-tube heat exchanger according to another embodiment of the present invention. (A) And (b) is a schematic front view of a flat heat-transfer tube single-piece | unit, (c) is a schematic front view which shows the state which equipped the corrugated fin of the cross-sectional channel shape in the flow path of the lamination type heat exchanger.

  The EGR system which is the subject of the present invention is basically a system in which air introduced from a pipe 9 from an air filter (not shown) is introduced into an intercooler 7 via a turbocharger 2, A part of the exhaust gas is taken out from the exhaust pipe 3 of the exhaust system via the EGR gas pipe 5 and is returned to the intake system of the engine 1 again through the EGR gas cooling device (EGR cooler) 4 for recirculation. By adopting a method (air cooling method) in which the EGR gas cooling device 4 is cooled by the cooling air introduced from the intercooler 7 or the cooling air supplied from the outside (air cooling method), the thermal efficiency of the engine and the exhaust gas are reduced. Purified. Note that both the EGR valves 11 and 12 are not required, and only one of them is required.

The system configuration example will be specifically described below. First, the cooled EGR system of the first embodiment shown in FIG. 1 is the cooling air for the EGR gas cooling device (EGR cooler) 4 in the EGR system having the basic configuration described above. In this method, the cooling air introduced from the intercooler 7 is used, and the air introduced from the pipe 9 from the air filter (not shown) is compressed by the turbocharger 2 and the temperature rises. In the system in which the exhaust gas is cooled through 7 and introduced into the engine 1 through the intake pipe 6, a part of the exhaust gas of the engine 1 is sent from the exhaust pipe 3 of the exhaust system to the EGR valve 12 (not necessary when the EGR valve 11 is provided) and EGR gas. Take out via the pipe 5 and use the EGR gas cooling device 4 and the EGR valve 11 (if there is an EGR valve 12) ), The cooling air introduced from the intercooler 7 in the system that is circulated back to the intake system of the engine 1 via the cooling air pipe 13 is caused to flow into the EGR gas cooling device 4 via the cooling air pipe 13. .
That is, the cooled EGR system shown in FIG. 1 includes a cooling air pipe 13 that is branchedly connected to the intake pipe 6 that introduces the intake air supplied from the intercooler 7 into the engine 1, and is provided in the cooling air pipe 13. The cooling air supplied from the intercooler 7 through the compressor, blower or fan 14 is forced to flow through the EGR gas cooling device 4 to efficiently cool the high-temperature exhaust gas. . The cooling air flows through the EGR gas cooling device 4 and then is pumped by the fan 10 and returned to the exhaust pipe 3 to be introduced into a muffler (not shown). Further, both the compressor or blower or fan 14 provided in the cooling air pipe 13 and the fan 10 for returning the cooling air flowing through the EGR gas cooling device 4 to the exhaust pipe 3 are not necessarily required. Only one of them may be used.

Next, the cooled EGR system of the second embodiment shown in FIG. 2 adopts a system that uses cooling air supplied from the outside to the cooling air of the EGR gas cooling device (EGR cooler) 4. In the system in which the air introduced from the pipe 9 (not shown) is compressed by the turbocharger 2 and heated up, but is cooled through the intercooler 7 and supplied to the engine 1 through the intake pipe 6. A part of the exhaust gas is taken out from the exhaust pipe 3 of the exhaust system via the EGR valve 12 (not necessary when the EGR valve 11 is provided) and the EGR gas pipe 5, and is then supplied to the EGR gas cooling device 4 and the EGR valve 11 (EGR valve 12 The EGR gas cooling device 4 in the system for recirculation back to the intake system of the engine 1 via the The air in the Njinrumu through the cooling air pipe 13 is obtained by adapted to flow into the EGR gas cooling device 4.
In this cooled EGR system, high-temperature exhaust gas is produced by forcing the air in the outside or engine room through the EGR gas cooling device 4 through a compressor, fan or blower 14 provided in the cooling air pipe 13. This is a system that efficiently cools the battery. The cooling air flows through the EGR gas cooling device 4 and then is pumped by the fan 10 and directly discharged to the outside air. However, it may be introduced into the exhaust pipe 3 as in the first embodiment. Also in this system, the compressor or fan or blower 14 provided in the cooling air pipe 13 and the fan 10 for returning the cooling air flowing through the EGR gas cooling device 4 to the exhaust pipe 3 are necessarily required. Instead, only one of them may be used.

Further, the cooled EGR system of the third embodiment shown in FIG. 3 is configured by sequentially arranging a water-cooled EGR gas cooling device 4a and the air-cooled EGR gas cooling device 4 in series in the EGR cooling system, In the system in which air introduced from a pipe 9 from an air filter (not shown) is compressed by the turbocharger 2 and heated up, it is cooled through the intercooler 7 and introduced into the engine 1 through the intake pipe 6. A water-cooled EGR gas cooling device (precooler) 4a for cooling a part of the exhaust gas 1 from the exhaust pipe 3 of the exhaust system with the cooling water of the engine in the EGR gas pipe 5 and the air-cooled EGR gas cooling A device (aftercooler) 4 is arranged in series via an EGR valve 15, and a part of the exhaust gas of the engine 1 is sent to the water-cooled EGR gas cooling device (pump). Is a system that circulates back again to the intake system of the engine 1 via a cooler) 4a and air-cooled EGR gas cooling device (aftercooler) 4. An engine cooling water pipe 16 is connected to the inflow side and the outflow side of the water-cooled EGR gas cooling device (precooler) 4a in this cooled EGR system, and the air-cooled EGR gas cooling device 4 is connected to the outside of the inflow side. A cooling air pipe 13 for introducing cooling air from is connected.
In this cooled EGR system, a part of the exhaust gas of the engine 1 taken out from the exhaust pipe 3 of the exhaust system via the EGR gas pipe 5 is first cooled by the water-cooled EGR gas cooling device (precooler) 4a. Cooling with water, and further cooling with an air-cooled EGR gas cooling device (aftercooler) 4 connected through an EGR valve 15. The air-cooled EGR gas cooling device 4 forcibly passes cooling air from the outside to the EGR gas cooling device 4 through the compressor, fan, blower 14 and the like provided in the cooling air pipe 13 as described above. By letting it flow, the exhaust gas can be efficiently cooled.
The exhaust gas of the engine 1 cooled by the two EGR gas cooling devices 4a and 4 is controlled by the EGR valve 15 so as to be returned to the intake system of the engine 1 and recirculated. The cooling air of the EGR gas cooling device 4 of the type is configured to flow through the cooling device, then return to the exhaust pipe 3 by the fan 10 and be introduced into a muffler (not shown). Also in this system, the compressor or fan or blower 14 provided in the cooling air pipe 13 and the fan 10 for returning the cooling air flowing through the EGR gas cooling device 4 to the exhaust pipe 3 are necessarily required. Instead, only one of them may be used.
In the present embodiment, since the EGR gas is cooled in advance by the precooler 4a, the temperature difference between the EGR gas and the cooling air in the aftercooler 4 is not so large and the EGR gas is not supercooled. Therefore, since EGR gas does not condense on the inner surface of the heat transfer tube, various problems due to condensation do not occur as described above.

The cooled EGR system of the fourth embodiment shown in FIG. 4 includes a water-cooled EGR gas cooling device (precooler) 4a arranged in series with the exhaust pipe 3 of the exhaust system in the EGR system shown in FIG. The configuration of the EGR gas cooling device 4 is substantially the same as that of the EGR system shown in FIG. In other words, the air-cooled EGR gas cooling device 4 and the water-cooled EGR gas cooling device 4a are sequentially arranged in series in the EGR cooling system, and are introduced from a pipe 9 from an air filter (not shown). The air that is compressed by the turbocharger 2 rises in temperature, but is cooled through the intercooler 7 and supplied to the engine 1 through the intake pipe 6. In the method of supplying a part of the exhaust gas of the engine 1 to the exhaust pipe 3 of the exhaust system. An air-cooled EGR gas cooling device (precooler) 4 and a water-cooled EGR gas cooling device (aftercooler) 4a that is cooled by engine cooling water are connected in series via an EGR valve 15 to the EGR gas pipe 5 to be taken out. The air-cooled EGR gas cooling device (precooler) 4 and the water-cooled EGR gas cooling device It is a system for recirculating back again to the intake system of the engine 1 via the (aftercooler) 4a. Similarly to the above, the water-cooled EGR gas cooling device (aftercooler) 4a in this cooled EGR system has an engine cooling water pipe 16 connected to the inflow side and the outflow side, and the air-cooled EGR gas cooling device 4 has its inflow side. A cooling air pipe 13 for introducing external cooling air is connected to the first and second cooling air pipes.
In this cooled EGR system, a part of the exhaust gas of the engine 1 taken out from the exhaust pipe 3 of the exhaust system via the EGR gas pipe 5 is first cooled by an air-cooled EGR gas cooling device (precooler) 4. The engine 1 is cooled by cooling air introduced from the outside through a compressor or fan or blower 14 provided in the engine 13 and then connected with an EGR valve 15 through a water-cooled EGR gas cooling device (aftercooler) 4a. Therefore, a part of the exhaust gas of the engine 1 can be cooled more efficiently as in the above system.
The exhaust gas of the engine 1 efficiently cooled by the two EGR gas cooling devices 4a and 4 is controlled by the EGR valve 15 so as to be returned to the intake system of the engine 1 and recirculated. The cooling air of the air-cooled EGR gas cooling device 4 flows through the cooling device and is then discharged to the outside by the fan 10. In the present embodiment, since the precooler 4 is air-cooled, the temperature of the EGR gas is high, and the temperature difference with the cooling air is large, so that the heat exchange performance is good and the precooler 4 can be downsized. Boiling phenomenon on the heat transfer tube surface on the EGR gas inflow side can be prevented as in the case of water cooling when the EGR gas temperature suddenly rises or the flow rate suddenly increases, so there is no sudden decline in heat exchange characteristics due to boiling. Performance is stable.

  Next, the structure of the multi-tube heat exchanger constituting the air-cooled EGR gas cooling device 4 according to the present invention will be described. The multi-tube heat exchanger 21 shown in FIGS. Inside the rectangular shell body 22, a plurality of flat heat transfer tubes 23 with corrugated fins 25 are attached via a tube sheet 22-1, maintaining a specific distance, and a fin structure 24 comprising a plurality of flat coil springs is attached. Arranged in contact with the outer peripheral surface of the flat heat transfer tube 23 adjacent to the inner peripheral surface of the shell main body 22 and the adjacent outer peripheral surface of the flat heat transfer tube 23, and adjusted so that the pitch interval is within a predetermined range. Then, it is configured to be heated and fixed as a unit by brazing. In the figure, A-1 is a cooling air inlet, A-2 is a cooling air outlet, and g is a flow of EGR gas.

  The flat heat transfer tube 23 in the multi-tube heat exchanger 21 uses, for example, a circular tube made of SUS316 austenitic stainless steel having a thickness of 0.5 mm, and presses the circular tube with a mold. A cross-sectional shape as shown in FIG. 7 forms a racetrack-shaped flat heat transfer tube main body 23-1, and a U-shaped cross-section as shown in FIG. The corrugated fin 25 having a plurality of notches 25-1 at a predetermined location showing a wave shape in the longitudinal direction and having a waveform in the longitudinal direction. The corrugated fins 25 are made of, for example, a SUS316 austenitic stainless steel of the same type as the flat heat transfer tube main body 23-1, made of a thin plate having a thickness of 0.2 mm, and are formed by press forming the thin metal plate. The interior of the flat heat transfer tube main body 23-1 is tightly joined by brazing.

  Further, the multi-tube heat exchanger 21a shown in FIGS. 9 and 10 has the multi-tube shown in FIGS. 5 and 6 except that the flat coil spring 26a shown in FIG. 10 is used instead of the corrugated fin 25. 10 has a configuration similar to that of the heat exchanger 21 and has a fin structure including a flat coil spring 26a shown in FIG. 10 instead of the corrugated fin 25 inside a shell body 22a having a substantially rectangular cross-sectional shape. A plurality of flat heat transfer tubes 23a having an internal body 26 are attached while maintaining a specific interval, and a fin structure 26 composed of a plurality of flat coil springs 26a is attached to the outer peripheral surface of the flat heat transfer tube 23a adjacent to the inner peripheral surface of the shell body 22a. Are arranged in contact with the outer peripheral surfaces of the adjacent flat heat transfer tubes 23a, adjusted so that the pitch interval is within a predetermined range, and then heated and brazed. Those constructed by fixing integrally Te.

  The flat heat transfer tube 23a in the multi-tube heat exchanger 21a is, for example, SUS316 austenitic stainless steel having a thickness of 0.5 mm, similar to the flat heat transfer tube 23 of the multi-tube heat exchanger 21 shown in FIGS. A circular heat transfer tube body 23a-1 having a racetrack shape in cross-section as shown in FIGS. 9 and 10 is formed by applying a pressing process to the circular tube using a mold. FIG. 10B shows the concave groove 23a-2 of the flat heat transfer tube 23a shown in FIG. 10A in which the concave groove 23a-2 is formed on the inner peripheral wall surface in the width direction by pressing with a mold. A fin structure 26 composed of a flat coil spring 26a is provided so that the wires are kept at a specific distance, and are integrally joined by brazing.

  The fin structures 24 and 26 are made of SUS316 austenitic stainless steel wires 24a to 24h processed into a cross-sectional shape shown in FIGS. 12A to 12H by cold drawing, as described above. 11 (a) to 11 (e), after the cross-sectional shape wound by applying close-contact winding to the wire is formed into a circular coil shape, pressing is performed between parallel surfaces using a mold. And a plurality of flat coil springs 20a, 20bd, 20c, 20d, and 20e having various wound cross-sectional shapes as shown in FIG.

  Note that the metal wire forming the coil spring to be the fin structure in the present invention is not particularly limited in its cross-sectional shape as long as it is a wire that can form the coil spring. A circle 24a shown in (a), a substantially oval shape 24b shown in (b), a substantially oval shape 24c shown in (c), a square 24d shown in (d), and (e) shown in FIG. Examples include a substantially rectangular shape 24e, a substantially pentagonal shape 24f shown in the same figure (f), a substantially hexagonal shape 24g shown in the same figure (g), and a substantially star shape 24h shown in the same figure (h). Any other shape can be adopted as long as it is along.

  Further, the method of disposing the fin structure on the inner peripheral surface of the shell main body and / or the outer peripheral surface of the flat heat transfer tube is arbitrary and is not particularly limited, but is shown in FIGS. 5, 6, 9, and 10. Thus, it is common to fix the flat heat transfer tube in a parallel, corrugated, vertical, or diagonal direction, or an arbitrary combination of these forms and then fixing them. Further, the winding cross-sectional shape of the fin structure to be disposed is not necessarily the same, and the winding cross-sectional shape of the coil spring forming the fin structure is, for example, a substantially oval shape in FIG. It is also arbitrary that it is a substantially rectangular shape in FIG. 5E, and the arrangement and combination thereof can be freely selected.

  Furthermore, as the shape of the flat heat transfer tube 23, not only the race track shape as shown in FIG. 13A but also the flat heat transfer tube 23b having a rectangular cross section as shown in FIG. Etc. can also be adopted. Moreover, as a shape of the shell main body 22, as shown to the same figure (c), it can be set as the laminated | stacked shell main body 22b which laminated | stacked the flat heat exchanger tube 23b whose cross-sectional shape is a rectangle.

  In the present invention, the metal material forming the corrugated fins 25 installed in the shell bodies 22, 22a, 22b and the flat heat transfer tubes 23 has a certain mechanical strength in addition to SUS316 austenitic stainless steel. As long as the material is excellent in heat resistance, corrosion resistance and heat transfer, and has good workability, it does not prevent proper selection from other metal materials, and a fin structure comprising a coil spring or a flat coil spring 26a As the metal wires forming the bodies 24 and 26, aluminum, copper, iron, titanium, nickel and alloys based on these are adopted in addition to the above-mentioned stainless steel, but certain corrosion resistance and excellent rigidity Austenitic stainless steel is more preferable because it can be suitably used for brazing and other joining. Used properly, it is also possible to use a subjected to a surface treatment plating or thermal spraying to these metals. Furthermore, although the wire forming means is a wire obtained by cold drawing, a wire obtained by other methods can be used. Further, although the flat heat transfer tubes 23 and 23a are formed by pressing with a mold using a circular tube, for example, a middle fitting type (single alignment or double alignment) is adopted by sheet metal processing using a flat plate. It doesn't prevent it. On the other hand, in this embodiment, brazing is adopted as a joining means for the fin structures 24 and 26 to the inner peripheral surface of the shell main bodies 22 and 22a and the outer peripheral surface of the flat heat transfer tubes 23 and 23a. It is not limited, and welding, diffusion bonding, and other joining means can be appropriately employed. Furthermore, prior to brazing, the joining wall surfaces of the fin structures 24 and 26 or the flat heat transfer tubes 23 and 23a are used. Of these, at least one of them may be plated in advance, and a paste, a wire, a foil or the like can be supplied to the bonding surface.

  According to the cooled EGR system configured by adopting the air-cooled EGR gas cooling device including the multi-tube heat exchanger shown in the above-described embodiment according to the present invention, the air-cooled EGR gas cooling device is forcibly passed. The flowing cooling air is effectively agitated by the edge effect of the fin structures 24 and 26 disposed in the multi-tube heat exchanger 21 constituting the cooler, and further, the fin structures 24 and 26 are The formed coil spring acts to continuously form a Karman vortex street, and the flow of air flowing outside the flat heat transfer tubes 23 and 23a is turbulent and excellent cooling effect. On the other hand, the high-temperature EGR gas flowing through the heat transfer tube is caused by the action of the corrugated fin 25, the notch 25-1 provided in the corrugated fin 25, and the flat coil spring 26a. Thus, since the flow velocity distribution is made uniform while receiving an appropriate stirring action, contact with the wall surfaces of the heat transfer tubes 23 and 23a is repeated evenly, and effective heat exchange with the air flowing outside thereof is performed. This results in excellent cooling performance and high temperature efficiency.

The cooled EGR system of the present invention is a system in which the EGR gas cooling device cools with cooling air introduced from an intercooler or cooling air introduced from the outside, and the cooling air is inflow side of the EGR gas cooling device. By adopting a multi-tubular heat exchanger that is forced to flow by a compressor, fan or blower provided in the EGR gas cooling device and has excellent heat exchange performance in an EGR gas cooling device (EGR cooler) It shows temperature efficiency and can further improve the thermal efficiency of the engine. When an EGR gas cooling system is configured by arranging an air cooling system and a water cooling system in series as an EGR gas cooling device (EGR cooler) in series, when using an air cooling EGR gas cooling device for the precooler, Since there is no boiling phenomenon at the EGR gas inlet as in the system, there is no sudden decrease in heat transfer. On the other hand, when an air-cooled EGR gas cooling device is used for the aftercooler, an EGR gas outlet as in the water-cooled system Condensation due to overcooling in the pipe does not occur on the inner surface of the heat transfer tube, so that deterioration of the heat transfer tube and engine parts due to corrosion is prevented.
Furthermore, this EGR system heat exchanger is an EGR cooler in an EGR gas cooling system because excellent cooling efficiency is effectively ensured despite the air-to-air heat exchange type multi-tube heat exchanger. As a matter of course, it is expected to be widely adopted as a heat exchanger for other cooling devices, and it is easily incorporated into the EGR system, and its excellent heat exchange performance reduces the size and weight of these devices. The EGR gas cooling system with outstanding layout characteristics is expected to be used in a wide range of industries because it can be easily installed in a limited space. Is done. Furthermore, the cooled EGR system that employs the air-to-air heat exchange type multi-tube heat exchanger of the present invention is a component that constitutes the cooling system as compared to the conventional cooled EGR system that employs only a water-cooled EGR cooler. As well as being able to reduce the size and weight, etc., and obtain excellent heat exchange performance, it contributes to the reduction of the size and weight of the onboard engine and the weight of the vehicle, greatly contributing to the prevention of global warming. obtain. Furthermore, the heat exchanger of the present invention is not limited to an air-cooled EGR cooler, and can be used for a wide range of applications such as an exhaust gas heat exchanger.

1 is a schematic view showing a first embodiment of a cooled EGR system according to the present invention. It is the schematic which shows the 2nd Example of a cooled EGR system similarly. It is the schematic which shows 3rd Example of a cooled EGR system similarly. It is the schematic which shows 4th Example of a cooled EGR system similarly. 1 is a schematic longitudinal sectional front view showing an embodiment of a multi-tube heat exchanger according to the present invention. It is a principal part vertical side view of a multitubular heat exchanger same as the above. It is a schematic perspective view which partially cuts and shows the flat heat exchanger tube incorporated in a multitubular heat exchanger same as the above. It is a schematic perspective view which shows the corrugated fin of the waveform corrugated previously by the flat heat exchanger tube same as the above. It is a general | schematic longitudinal cross-section front view which shows a part of other Example of the multi-tube heat exchanger which concerns on this invention. It is the schematic which shows the single unit of the flat heat exchanger tube integrated in the multi-tube heat exchanger shown in FIG. 9, (a) is a partial abbreviation perspective view of the flat heat exchanger tube which comprised the flat coil spring, (b) is a flat coil. It is a perspective view with partial omission of a single spring. The example of the cross-sectional shape wound of the fin structure which consists of a coil spring which concerns on this invention is shown, (a)-(e) is the front view which illustrated the state which formed the wound cross-sectional shape flatly. The cross-sectional shape of the metal wire which forms the coil spring used as a fin structure same as the above is shown, (a)-(h) is sectional drawing which illustrated the cross-sectional shape. The flat heat exchanger tube arrange | positioned at the multitubular heat exchanger which concerns on the other Example of this invention is shown, (a) And (b) is a schematic front view of a flat heat exchanger tube, (c) is a laminated type. It is a schematic front view which shows the state which equipped the corrugated fin of the cross-sectional channel shape in the flow path of the heat exchanger. It is a schematic longitudinal side view for demonstrating the conventional shell and tube type multi-tube heat exchanger. FIG. 12 shows a flat heat transfer tube and a shell body with corrugated plate fins having a rectangular cross section mounted on the multitubular heat exchanger shown in FIG. 12, (a) is a schematic front view thereof, and (b) is a flat heat transfer tube alone. FIG. 2C is a schematic plan view of a plate fin installed in the flat heat transfer tube.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Turbocharger 3 Exhaust pipe 4, 4a EGR cooler 5 EGR gas piping 6 Intake pipe 7 Intercooler 8 Radiator 9 Piping from an air filter 10 Fan 11, 12, 15 EGR valve 13 Cooling air piping 14 Compressor, fan, blower 16 Engine cooling water piping 21, 21a Multi-tube heat exchangers 22, 22a, 22b Shell body 22-1 Tube sheets 23, 23a, 23b Flat heat transfer tubes 24, 26 Fin structure 25 Corrugated fin 26a Flat coil spring

Claims (15)

  In the EGR system, a part of the exhaust gas is taken out from the exhaust system as EGR gas, cooled by the EGR gas cooling device, and returned to the engine intake system again. In the EGR system, the cooling air introduced from the intercooler or the outside Cooled EGR system characterized by being cooled by cooling air supplied from   The cooled EGR system according to claim 1, wherein the cooling air is forced to flow by a compressor, a fan, or a blower provided on an inflow side of the EGR gas cooling device.   The cooled EGR system according to claim 1 or 2, wherein a water-cooled EGR gas cooling device is incorporated upstream or downstream of the air-cooled EGR gas cooling device.   The cooled EGR system according to any one of claims 1 to 3, wherein the air-cooled EGR gas cooling device is a multi-tube heat exchanger.   The air-cooled EGR gas cooling device is a multi-tube heat exchanger in which a plurality of flat heat transfer tubes are arranged at intervals in a shell body having a rectangular cross-sectional shape. The cooled EGR system according to any one of 1 to 3.   In a multi-tubular heat exchanger in which a plurality of flat heat transfer tubes are arranged at intervals in a shell body having a rectangular cross section, a space generated between the inner peripheral surface of the shell main body and the outer peripheral surface of the flat heat transfer tube adjacent thereto. And at least one of fin structures made of a coil spring formed by winding a wire rod in a spiral shape in a space formed between the outer peripheral surfaces of adjacent flat tubes. A cooled EGR system, wherein the fin structure is closely attached to and fixed to the outer peripheral surface of the flat heat transfer tube adjacent to the inner peripheral surface of the shell main body and / or to the outer peripheral surfaces of the adjacent flat heat transfer tubes adjacent to each other at a predetermined interval. Multitubular heat exchanger.   The multi-tubular heat for a cooled EGR system according to claim 6, wherein the fin structure including the coil spring is a flat coil spring having a flat cross-sectional shape obtained by winding the wire rod in a spiral shape. Exchanger.   The multi-tubular heat exchanger for a cooled EGR system according to claim 6, wherein a corrugated fin having a cross-sectional channel shape is preliminarily incorporated in the flat heat transfer tube.   The multi-tube heat exchanger for a cooled EGR system according to claim 6, wherein the flat heat transfer tube is internally provided with a fin structure including the flat coil spring.   A space formed between the outer peripheral surfaces of the flat heat transfer tubes adjacent to the inner peripheral surface of the shell body and a space formed between the outer peripheral surfaces of the adjacent flat heat transfer tubes, the fin structure comprising the coil spring or the flat coil spring; In the flat heat transfer tube, the flat heat transfer tube is closely attached and fixed in a parallel, corrugated, vertical, or oblique form, or any combination thereof. The multitubular heat exchanger for a cooled EGR system according to any one of claims 6 to 9.   The means for fixing the fin structure comprising the coil spring or the flat coil spring to the inner peripheral surface of the shell body and / or the outer peripheral surface of the flat heat transfer tube is appropriately selected from welding, brazing, diffusion and other joining means. The multi-tubular heat exchanger for a cooled EGR system according to claim 10, wherein the multi-tubular heat exchanger is fixed by being tightly and integrally joined.   The coil spring or the flat coil spring forming the fin structure is made of a metal wire, and is wound so that a pitch interval generated between the wires is 2 to 10 mm, and the wound cross-sectional shape is flat. The multitubular heat exchanger for a cooled EGR system according to any one of claims 7 and 9 to 11, wherein the multitubular heat exchanger is one of a substantially oval shape, a substantially oval shape, a substantially rectangular shape, and a substantially hexagonal shape.   The cross-section of the metal wire forming the coil spring or the flat coil spring is arbitrarily deformed based on a circle or a substantially oval, a substantially oval, a triangle, a square, or a square arbitrarily deformed based on the circle. The cooled EGR system according to claim 7, having a cross-sectional shape selected from a substantially rectangular shape, a substantially pentagonal shape, a substantially hexagonal shape, a substantially polygonal shape, a star shape, and the like. Multitubular heat exchanger.   The metal wire forming the coil spring or the flat coil spring is made of stainless steel, aluminum, copper, iron, titanium, nickel and alloys based on these, and these metals are subjected to surface treatment as desired. The multitubular heat exchanger for a cooled EGR system according to any one of claims 7 and 9 to 13.   The cooling medium passes through the flow path formed in the space between the inner peripheral surface of the shell main body and the outer peripheral surface of the flat heat transfer tube, and the cooling medium passes through the flow path formed in the inner peripheral surface of the flat heat transfer tube. The multi-tube heat exchanger for a cooled EGR system according to any one of claims 6 to 14, wherein the medium is cooling air and the medium to be cooled is exhaust gas.