JP2007315324A - Cooling structure of egr cooler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling structure of an EGR cooler, capable of restraining local boiling by a two-piece type, capable of preventing reduction in durability, and capable of enhancing the whole heat exchange efficiency. <P>SOLUTION: Two heat exchangers are formed by adding a cooling water outlet to a heat exchanger outer shell on the side for arranging a cooling water inlet, and adding the cooling water inlet to a heat exchanger outer shell on the side for arranging the cooling water outlet, in a position of the heat exchanger outer shell corresponding to these divided respective spaces, by axially dividing the respective tube outer peripheral side spaces, by adding a partition plate to a central part in the axial direction in a tube assembly stored in the heat exchanger outer shell; and are constituted by connecting an engine cooling water pipe connected to the high temperature side heat exchanger for passing EGR gas first and the low temperature side heat exchanger for passing the EGR gas after this heat exchanger, among these two heat exchangers, so as to cool the high temperature side heat exchanger after cooling the low temperature side heat exchanger. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cooling structure of an EGR cooler that can improve cooling efficiency by providing a baffle plate in a cooling water passage and dividing it.

In recent years, with the tightening of exhaust gas regulations for diesel engines, the environment surrounding the EGR cooler has become severe, such as an increase in the temperature of the EGR gas, an increase in gas flow rate, and a decrease in the gas outlet temperature of the EGR cooler (an increase in heat dissipation). It is desired to increase the amount of heat and maintain high temperature durability.
In general, as shown in FIG. 5, an intercooler 2 and a radiator 3 are arranged in front of a diesel engine 1, an EGR cooler 4 or 6 is arranged in the rear, and a turbocharger 5 is arranged in the side. Then, the turbocharger 5 is arranged so that the compressor 5a is directed to intake air from the front and exhaust gas from the turbine 5b is discharged backward.
In ordinary EGR coolers 4 and 6, a multi-tubular heat exchanger incorporating a large number of circular tubes shown in FIG. 6 or a flat tube heat exchanger incorporating a large number of flat tubes provided with radiating fins shown in FIG. As shown, the cooling water inlets 4a, 6a are provided at the end on the gas inlet side, the cooling water outlets 4b, 6b are provided at the end on the gas discharge side, and the flanged headers 4c, 4d, 6c, and 6d are provided, and the sizes of the flanges 4e, 4f, 6e, and 6f are determined so that they can be bolted to the piping from the diesel engine 1 side.
As shown in FIG. 8, the internal structure of the EGR coolers 4 and 6 includes a plurality of tubes 4i,..., 4i, 6i,. A multi-tubular heat exchanger or flattening that incorporates a tube assembly 7 that is supported with 6g and outlet side partition plates 4h and 6h being closed so that the intervals between the tubes are substantially evenly spaced from each other. It is configured as a tube heat exchanger.
The relationship between the inlet and outlet of the exhaust gas to the EGR coolers 4 and 6 and the inlet and outlet of the cooling water is that the cooling water inlets 4a and 6a are provided at the end on the gas inlet side, and the cooling water outlet 4b is provided at the end on the gas outlet side. , 6b is provided (cocurrent flow cooling method) that is devised so that the flow flows evenly in the main body by the pressure of cooling water (Patent Document 1). There is also a cooling water inlet 4a, 6a provided on the gas discharge side and a cooling water outlet 4b, 6b provided on the gas inlet side (counterflow cooling method) (Patent Document 2).

JP 2000-045883 A JP 2000-274990 A

[Problems of the prior art]
In the EGR coolers 4 and 6, since the cooling water after cooling the diesel engine 1 is normally used, the cooling water inlet temperature is approximately 80 ° C. to 90 ° C., and the exhaust gas temperature is on the gas inlet side. The temperature difference between the two fluids is large near the gas inlet side at a high temperature of 500 ° C. or more at the end of the gas, and the temperature of the cooling water locally rises near the boiling point, and in some cases, it may boil.
In order to suppress this boiling, the cooling water inlets 4a and 6a are provided at the gas inlet side ends of the EGR coolers 4 and 6, and the cooling water outlets 4b and 6b are provided at the gas outlet side ends. Some have a structure in which the flow is evenly diffused by the inflowing pressure. In the case of this structure, since the flow of EGR gas and cooling water is in the same direction, the temperature difference between the two fluids decreases due to the decrease in gas temperature and the increase in cooling water temperature toward the outlet, and the heat exchange amount decreases. .
On the other hand, it is considered that the heat exchanger is divided into two in the longitudinal direction. However, if the same cooling water is used, the temperature on the inlet side does not change, and the piping system on both the inlet side and the outlet side is changed. As a result, the pipes are complicated and the installation work becomes difficult.

  The present invention has been made in view of the above problems in the prior art, and the technical problem specifically set in order to solve this problem is to divide local boiling in the longitudinal direction of the cooling water channel. An object of the present invention is to provide a cooling structure for an EGR cooler that can suppress, prevent deterioration of durability, and increase the overall heat exchange efficiency.

In order to specify the cooling structure of the EGR cooler that effectively solves the above-mentioned problems in the present invention, all the matters recognized as necessary are covered and specifically configured as the problem solving means.
The first problem-solving means related to the cooling structure of the EGR cooler is a tube in which a large number of tubes of the same length are parallel and the tubes are supported at both ends by partition plates in a state where the tubes are spaced from each other. The assembly is accommodated inside a cylindrical heat exchanger outer shell, and a cooling water inlet and a cooling water outlet are provided in the heat exchanger outer shell, and EGR gas passes through each tube to cool each tube outer periphery. A cooling structure of an EGR cooler having a tube heat exchanger cooled by water, wherein a partition plate is added to the axial center of the tube assembly to divide the space on the outer periphery side of each tube in the axial direction. At the position of the heat exchanger outer shell corresponding to each space, a cooling water outlet is added to the heat exchanger outer shell provided with the cooling water inlet, and the heat of the one provided with the cooling water outlet is added. Exchanger shell Adds two cooling water inlets to form two heat exchangers, and of these two heat exchangers, a high temperature side heat exchanger through which EGR gas passes first, and a low temperature side heat exchanger through which EGR gas passes thereafter The engine cooling water pipe connected to is connected to cool the high temperature side heat exchanger after cooling the low temperature side heat exchanger.

The second problem-solving means related to the cooling structure of the EGR cooler is the same as that described above, wherein the cooling water inlet of the high temperature side heat exchanger and the cooling water outlet of the low temperature side heat exchanger are connected by a relay pipe. Connect the engine cooling water supply side piping to the cooling water inlet of the side heat exchanger, connect the engine cooling water discharge side piping to the cooling water outlet of the high temperature side heat exchanger, and connect the low temperature side heat exchanger It flows from the cooling water inlet and flows out from the cooling water outlet of the high temperature side heat exchanger.
Further, the third problem-solving means related to the cooling structure of the EGR cooler is the same as that described above, in the high-temperature side heat exchanger, a cooling water inlet is arranged on the EGR gas inlet side and a cooling water outlet is arranged on the EGR gas outlet side. The low temperature side heat exchanger is provided with a cooling water inlet on the EGR gas outlet side and a cooling water outlet on the EGR gas inlet side. The apparatus is characterized by countercurrent cooling.
Furthermore, the fourth problem-solving means according to the cooling structure of the EGR cooler is to set the division ratio between the low-temperature side heat exchanger and the high-temperature side heat exchanger within the range of 1: 9 to 5: 5. Features.

  In the first problem-solving means relating to the cooling structure of the EGR cooler, after providing a high-temperature side heat exchanger and a low-temperature side heat exchanger and cooling the low-temperature side heat exchanger first using the same cooling water, By cooling the high-temperature side heat exchanger, even if it has two, a high-temperature side heat exchanger and a low-temperature side heat exchanger, local boiling is suppressed to prevent deterioration in durability and increase overall heat exchange efficiency. be able to.

  In the second problem solving means relating to the cooling structure of the EGR cooler, the cooling water outlet provided in the low temperature side heat exchanger and the cooling water inlet provided in the high temperature side heat exchanger are connected by a relay pipe, and the same cooling water is used. Thus, after cooling the low-temperature side heat exchanger first, the high-temperature side heat exchanger is cooled to increase the heat exchange amount, and the cooling efficiency can be increased, and the two heat exchangers can be combined in a compact manner.

In the third problem solving means relating to the cooling structure of the EGR cooler, the high-temperature side heat exchanger is used as cocurrent cooling and the low-temperature side heat exchanger is used as countercurrent cooling. Using dynamic pressure to improve the spread of water, suppress local boiling, prevent durability such as tube exposure, low temperature side heat exchanger can lower the minimum temperature, using the same cooling water By increasing the amount of heat exchange, cooling efficiency can be increased, temperature management can be facilitated, and cooling efficiency can be increased.
Moreover, in the 4th problem-solving means which concerns on the cooling structure of an EGR cooler, by making the division | segmentation ratio of a low temperature side heat exchanger and a high temperature side heat exchanger into the range of 1: 9-5: 5, EGR cooler In addition, the heat radiation amount of the low-temperature side heat exchanger can be made relatively small and the water temperature rise can be kept relatively small. When the split ratio approaches 5: 5, the heat dissipation amount of the low-temperature side heat exchanger increases, but it is within the allowable range of 20% or less, and the position of the partition plate that divides the core is closer to the center. Etc. becomes easy and advantageous in terms of work.

Hereinafter, the best embodiment according to the present invention will be described in detail.
However, this embodiment is specifically described for better understanding of the gist of the invention, and does not limit the content of the invention unless otherwise specified.
In addition, the same thing as a prior art example attaches | subjects the same code | symbol, and abbreviate | omits detailed description.

“First Embodiment”
〔Constitution〕
The EGR cooler 8 of the first embodiment replaces the baffle plate provided in the cooling water flow path of one heat exchanger main body with a partition plate 8j as shown in the multi-tube heat exchanger of FIG. Each chamber partitioned by is sealed without gaps, and the longitudinal direction (flow direction) of the cooling water flow path is bisected. With this partition plate 8j as a boundary, the side positioned on the EGR gas inlet side is used as the high temperature side heat exchanger 8a, and the side positioned on the EGR gas outlet side is used as the low temperature side heat exchanger 8b.
In this EGR cooler 8, cooling water inlets 14a and 24a and cooling water outlets 14b and 24b are respectively attached to the high temperature side heat exchanger 8a and the low temperature side heat exchanger 8b, and the cooling provided in the high temperature side heat exchanger 8a. By connecting the water inlet 14a and the cooling water outlet 24b provided in the low temperature side heat exchanger 8b with the relay pipe 8k, the engine cooling water can be supplied from the low temperature side heat exchanger 8b to the high temperature side heat exchanger 8a. It can be so.

In this EGR cooler 8, only the cooling water flow path is partitioned by the partition plate 8j, and the gas flow path includes the high temperature side heat exchanger 8a and the low temperature side heat exchanger 8b. The tubes 17 and 27 are formed of the same tube from the high temperature side heat exchanger 8a to the low temperature side heat exchanger 8b, and EGR gas flows into the low temperature side heat exchanger 8b immediately after passing through the high temperature side heat exchanger 8a. Thus, heat loss does not occur in the middle and the heat exchange efficiency does not decrease.
Therefore, when the high temperature side heat exchanger 8a and the low temperature side heat exchanger 8b flow in and out the engine cooling water from the cooling water inlet and the cooling water outlet of the heat exchangers 8a and 8b, respectively, When forming a piping system in which the inlet 14a and the cooling water outlet 24b are connected by the relay pipe 8k, the high temperature side heat exchanger 8a is cocurrent cooling, and the low temperature side heat exchanger 8b is countercurrent cooling.

  If the high-temperature side heat exchanger 8a is cooled in parallel flow, and the local pressure is suppressed by using the dynamic pressure when the cooling water flows in, the local boiling is suppressed, and the tubes 17,. It is possible to eliminate a factor that deteriorates durability such as exposure of 17. Further, in the low temperature side heat exchanger 8b, when the EGR gas temperature is set to 200 ° C. or less, preferably around 150 ° C. at the EGR gas inlet portion in the tubes 27,. Thus, it is possible to effectively cool, maintain high efficiency as a heat exchanger, lower the EGR gas outlet temperature, and lower the minimum temperature than before.

“Second Embodiment”
〔Constitution〕
As shown in the flat tube heat exchanger of FIG. 2, the EGR cooler 9 of the second embodiment replaces the baffle plate provided in the cooling water flow path of one heat exchanger main body with a partition plate 9j, thereby dividing the partition plate 9j. Each chamber partitioned by is sealed without gaps, and the longitudinal direction (flow direction) of the cooling water flow path is bisected. With the partition plate 9j as a boundary, the side located on the EGR gas inlet side is used as the high temperature side heat exchanger 9a, and the side located on the EGR gas outlet side is used as the low temperature side heat exchanger 9b.
In this EGR cooler 9, cooling water inlets 34a and 44a and cooling water outlets 34b and 44b are respectively attached to the high temperature side heat exchanger 9a and the low temperature side heat exchanger 9b, and the cooling provided in the high temperature side heat exchanger 9a. The water inlet 34a and the cooling water outlet 44b provided in the low temperature side heat exchanger 9b are connected by a relay pipe (not shown), and the engine cooling water is transferred from the low temperature side heat exchanger 9b to the high temperature side heat exchanger 9a. To be able to supply.

In this EGR cooler 9, only the cooling water flow path is partitioned by the partition plate 9j, and the high temperature side heat exchanger 9a and the low temperature side heat exchanger 9b are provided with thin plate fins. Each of the flat tubes 37, 47 is formed by the same tube from the high temperature side heat exchanger 9a to the low temperature side heat exchanger 9b, and immediately after the EGR gas passes through the high temperature side heat exchanger 9a, the flat tube 37, 47 enters the low temperature side heat exchanger 9b. The heat exchange efficiency does not decrease due to heat loss on the way.
Therefore, when the high temperature side heat exchanger 9a and the low temperature side heat exchanger 9b flow in and out the engine cooling water from the cooling water inlet and the cooling water outlet of the respective heat exchangers 9a and 9b, the cooling water When forming a piping system in which the inlet 34a and the cooling water outlet 44b are connected by a relay pipe, the high temperature side heat exchanger 9a is cocurrent cooling, and the low temperature side heat exchanger 9b is countercurrent cooling.

  If the high temperature side heat exchanger 9a is cooled in parallel flow and the dynamic pressure at the time when the cooling water flows in is used to improve the spread of water and suppress local boiling, the tubes 37,. It is possible to eliminate a factor that deteriorates durability such as exposure of 37. Moreover, in the low temperature side heat exchanger 9b, if the EGR gas temperature is set to 200 ° C. or lower, preferably around 150 ° C. at the EGR gas inlet, it can be effectively cooled by using countercurrent cooling. Further, the efficiency as a heat exchanger can be kept high, the outlet temperature of the EGR gas can be lowered, and the minimum temperature can be made lower than before.

In the following, the effects common to the first and second embodiments will be described.
[Function and effect]
In the EGR cooler of each embodiment configured as described above, by dividing into two heat exchangers 8a and 8b or heat exchangers 9a and 9b on the high temperature side and the low temperature side with respect to the flow direction of the EGR gas, Not only can the heat exchange efficiency be improved more effectively, the deterioration of durability can be suppressed and the operating rate can be improved, but also the assembly can be facilitated and the cost can be reduced when assembled on the engine side.
Since the cooling efficiency slightly changes when the division ratio of the two divided heat exchangers is changed, the results of examining the change state are shown in FIGS.

In FIG. 3, comparison is made as a change in the length of the heat exchanger that makes the heat dissipation amount substantially the same. The horizontal axis represents the heat exchanger split ratio between the low temperature side and the high temperature side, and the vertical axis represents the heat exchanger. Indicates the length of the core part. Among them, the hatched portion indicates the low temperature side and the painted portion indicates the high temperature side.
In this case, if the division ratio of the low temperature side heat exchangers 8b and 9b is increased, the length of the heat exchanger can be slightly reduced, and the low temperature side: high temperature side division ratio is 1: 9-4. : The effect change is relatively large up to 6, but when the low temperature side becomes longer to a division ratio of 5: 5 or more, the effect reaches its peak.

FIG. 4 shows the ratio of the heat radiation amount of the low temperature side heat exchangers 8b and 9b to the total heat radiation amount of the heat exchanger. The ratio of the heat radiation amount of the low temperature side heat exchangers 8b and 9b increases as the division ratio of the low temperature side heat exchangers 8b and 9b increases, and the low temperature side heat exchanger even when the division ratio is 5: 5 or more. The ratio of the heat radiation amount of 8b and 9b is increasing.
On the other hand, since the cooling water temperature also rises in proportion to the increase in the heat radiation amount of the low temperature side heat exchangers 8b and 9b, the inlet temperature of the cooling water of the high temperature side heat exchangers 8a and 9a also rises. On the EGR gas inlet side of the high temperature side heat exchangers 8a and 9a, the gas temperature is high, and the risk of boiling due to an increase in the temperature of the cooling water also increases.

Therefore, it is necessary to select a range in which the heat radiation amount of the low-temperature side heat exchangers 8b and 9b is as small as possible. In view of these, the division ratio of the heat exchanger is as follows in the range of 1: 9 to 5: 5. These characteristics are suitable for use. That is,
(1) When the division ratio is in the range of 1: 9 to 2: 8, the heat radiation amount of the low-temperature side heat exchangers 8b and 9b is small, and there is an effect of division.
(2) When the split ratio is in the range of 3: 7 to 4: 6, the heat release of the low-temperature side heat exchangers 8b and 9b is around 10%, the water temperature rise is relatively small, and the split effect is large.
(3) When the split ratio is 5: 5, the heat radiation of the low-temperature side heat exchangers 8b and 9b is as large as 17%, but the position where the core is split is the center, which is advantageous in terms of ease of making positioning, etc. is there.

[Another aspect]
Such an embodiment is specifically described in order to facilitate understanding of the gist of the invention, but does not limit the content of the invention, and is not particularly described (including design content). The embodiment is not limited, and may be changed as appropriate. In this sense, some other embodiments that meet the spirit of the invention are shown below.

Although the high temperature side heat exchangers 8a and 9a are cocurrent cooling and the low temperature side heat exchangers 8b and 9b are countercurrent cooling, both are not necessarily formed in such a form, but both are cocurrent cooling or countercurrent cooling. However, it can be used if piping is easy and local boiling is suppressed without lowering heat exchange efficiency, durability is prevented from lowering, and overall heat exchange efficiency is increased.
In the illustrated example, a multi-tube heat exchanger or a flat tube heat exchanger is shown, but other types may be used. Further, although the cooling water is engine cooling water, cooling water dedicated to the EGR cooler cooled by a dedicated radiator may be used.
In this way, the structure can be divided into two heat exchangers, and the post-process including assembly can be processed efficiently, improving work efficiency, and contributing to cost reduction and heat exchange efficiency. If available.

1 is a partial cross-sectional perspective view showing an EGR cooler forming a multi-tube heat exchanger according to a first embodiment of the present invention. It is a fragmentary sectional perspective view which shows the EGR cooler which forms the flat tube type heat exchanger by the 2nd Embodiment of this invention. It is a graph which shows the effect by the heat exchanger division | segmentation of the EGR cooler in embodiment of this invention. It is a graph which shows the ratio of the low temperature side heat radiation amount of the EGR cooler by embodiment of this invention. It is a system system | strain diagram of the conventional EGR cooler. It is a perspective view which shows the EGR cooler which forms the conventional multitubular heat exchanger. It is a perspective view which shows the EGR cooler which forms the conventional flat tube type heat exchanger. It is longitudinal cross-sectional explanatory drawing which shows the internal structure of the heat exchanger used for the conventional EGR cooler.

Explanation of symbols

1 Diesel engine 2 Intercooler 3 Radiators 4, 6, 8, 9 EGR coolers 4a, 6a, 14a, 24a, 34a, 44a Cooling water inlets 4b, 6b, 14b, 24b, 34b, 44b Cooling water outlets 4g, 6g Inlet side Partition plates 4h, 6h Exit side partition plates 4i, 6i, 17, 27, 37, 47 Tube 5 Turbocharger 5a Compressor 5b Turbine 7 Tube assembly 8a, 9a High temperature side heat exchangers 8b, 9b Low temperature side heat exchangers 8j, 9j Partition plate 8k relay pipe

Claims (4)

Outside the heat exchanger in which a tube assembly is formed in a cylindrical shape, with both ends of each tube supported by a partition plate in a state where many tubes of the same length in the axial direction are parallel and the tubes are spaced from each other EGR having a tube-type heat exchanger that is accommodated in the shell, has a cooling water inlet and a cooling water outlet in the outer shell of the heat exchanger, passes EGR gas through each tube, and cools the outer periphery of each tube with cooling water A cooling structure of the cooler,
In the tube assembly, a partition plate is added to the central portion in the axial direction to divide the space on the outer periphery side of each tube in the axial direction, and a cooling water inlet is provided at the position of the heat exchanger outer shell corresponding to each of the divided spaces. A cooling water outlet is added to the outer heat exchanger shell provided, and a cooling water inlet is added to the outer heat exchanger shell provided with the cooling water outlet to form two heat exchangers. ,
Of these two heat exchangers, the engine cooling water pipe connected to the high temperature side heat exchanger through which the EGR gas first passes and the low temperature side heat exchanger through which the EGR gas passes thereafter is connected to the low temperature side heat exchange. A cooling structure for an EGR cooler, wherein the high-temperature side heat exchanger is connected to be cooled after the cooler is cooled.   Connect the cooling water inlet of the high temperature side heat exchanger and the cooling water outlet of the low temperature side heat exchanger with a relay pipe, and connect the engine cooling water supply side piping to the cooling water inlet of the low temperature side heat exchanger An engine cooling water discharge side pipe is connected to the cooling water outlet of the high temperature side heat exchanger, and flows in from the cooling water inlet of the low temperature side heat exchanger and from the cooling water outlet of the high temperature side heat exchanger. 2. The cooling structure for an EGR cooler according to claim 1, wherein the cooling structure flows out.   The high temperature side heat exchanger has a cooling water inlet on the EGR gas inlet side and a cooling water outlet on the EGR gas outlet side, and the low temperature side heat exchanger has a cooling water inlet on the EGR gas outlet side. The EGR according to claim 1, wherein a cooling water outlet is disposed on the EGR gas inlet side, the high temperature side heat exchanger is configured as cocurrent cooling, and the low temperature side heat exchanger is configured as countercurrent cooling. Cooler cooling structure.   The cooling structure of the EGR cooler according to claim 1, wherein a division ratio between the low temperature side heat exchanger and the high temperature side heat exchanger is in a range of 1: 9 to 5: 5.

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