JP2016044548A - EGR cooler - Google Patents

Abstract

An EGR cooler capable of suppressing corrosion of a cooling pipe during an engine stop period is provided.
An EGR cooler (27) includes a multi-tube type cooling unit (34) constituted by a plurality of cooling pipes (35). The cooling unit 34 includes a first cooling element 47 including a first cooling pipe 46 and a second cooling pipe 48 having higher corrosion resistance than the first cooling pipe 46, and the first is in a state where the EGR cooler 27 is mounted on the vehicle. And a second cooling element 49 positioned below the cooling element 47 in the vertical direction.
[Selection] Figure 2

Description

  The present invention relates to an EGR cooler that cools EGR gas.

  Conventionally, diesel engines are equipped with an exhaust gas recirculation (EGR) device that introduces part of the exhaust gas into the intake passage. Among EGR devices, there is also an EGR device that includes an EGR cooler that cools EGR gas in an EGR passage that connects an intake passage and an exhaust passage. The EGR cooler includes, for example, a multi-tube type cooling unit composed of a plurality of cooling pipes through which EGR gas flows, and circulates cooling water outside the plurality of cooling pipes, and cools the EGR gas and the cooling water through the cooling pipes. The EGR gas is cooled by heat exchange with water.

  By the way, in an EGR cooler provided with a multi-tube cooling unit, condensed water in which moisture contained in the EGR gas is condensed is generated in the cooling pipe as the EGR gas is cooled. A corrosive liquid is produced | generated by the sulfur dioxide in EGR gas etc. melt | dissolving in this condensed water. As a technique for suppressing the corrosion of the cooling pipe caused by such a corrosive liquid, Patent Document 1 discloses a first EGR cooler having a ceramic cooling pipe with high corrosion resistance and a second EGR cooler having a metal cooling pipe. An equipped EGR device is disclosed. In this EGR device, when the temperature of the cooling water is low and a condensate is easily generated in the cooling pipe, the EGR gas is preferentially circulated to the first EGR cooler provided with the ceramic cooling pipe.

JP 2013-36338 A

  On the other hand, the temperature of the EGR gas remaining in the EGR cooler when the engine is stopped decreases to the outside temperature over time. Therefore, condensed water is generated in the cooling pipe even when the engine is stopped. This condensed water may remain in the cooling pipe until the engine is driven. Therefore, it is desired to suppress the corrosion of the cooling pipe during the engine stop period.

  An object of this invention is to provide the EGR cooler which can suppress the corrosion of the cooling pipe in the engine stop period.

  An EGR cooler that solves the above-described problem includes a multi-tube type cooling unit including a plurality of cooling pipes, and the cooling unit includes a first cooling element that includes a first cooling pipe, and the first cooling pipe. A second cooling element that is made of a second cooling pipe having high corrosion resistance, and is located below the first cooling element in the vertical direction in a state where the EGR cooler is mounted on the vehicle.

  In the space where the EGR gas remains in the EGR cooler, condensed water is likely to be generated in the lower space in the vertical direction due to convection associated with the temperature drop of the EGR gas during the engine stop period. According to the above configuration, during the engine stop period, the condensed water is easily generated in the second cooling pipe having higher corrosion resistance than the first cooling pipe. Therefore, the corrosion of the cooling pipe during the engine stop period can be suppressed as compared with the case where the cooling unit is configured by only the first cooling pipe.

In the EGR cooler, it is preferable that the plurality of cooling pipes include the first cooling pipe and the second cooling pipe.
According to the above configuration, only two types of cooling pipes are required.
In the EGR cooler, it is preferable that the first cooling element includes the first cooling pipe.

  The cooling pipe tends to be more expensive as the cooling pipe has higher corrosion resistance. According to the said structure, a cooling part is comprised by the 1st cooling element which consists of a 1st cooling pipe, and the 2nd cooling element which consists of a 2nd cooling pipe. Therefore, the material cost of the EGR cooler can be reduced as compared with the case where the first cooling element includes the second cooling pipe.

In the EGR cooler, the ratio of the number of the second cooling pipes constituting the second cooling element to the total number of the cooling pipes included in the cooling unit is preferably ½ or less.
According to the above configuration, the material cost of the EGR cooler can be suppressed while suppressing the corrosion of the cooling pipe during the engine stop period.

In the EGR cooler, it is preferable that the first cooling pipe is a spiral tube and the second cooling pipe is a straight tube.
Since the first cooling pipe is a spiral tube and the second cooling pipe is a straight tube, the cooling efficiency of the EGR cooler is improved as compared with the case where each cooling pipe is a straight tube. Moreover, when the 1st cooling pipe and the 2nd cooling pipe have the same outer diameter, the freedom degree regarding thickness improves about the 2nd cooling pipe in which condensed water is easy to be produced | generated.

The figure which shows schematic structure of the EGR apparatus carrying one Embodiment of an EGR cooler with an engine. The figure which shows an example of the cross-section of an EGR cooler in the cross section along a perpendicular direction.

An embodiment of the EGR cooler will be described with reference to FIGS. 1 and 2.
First, a schematic configuration of an EGR device having an EGR cooler will be described together with an engine equipped with the EGR device.

  As shown in FIG. 1, the engine 10 includes a plurality of cylinders 12 aligned in a cylinder block 11. Connected to the cylinder block 11 are an intake manifold 14 for supplying a working gas, which is a mixed gas of intake air and EGR gas, to each cylinder 12, and an exhaust manifold 15 into which exhaust gas flows from each cylinder 12. Yes.

  In the intake passage 16 connected to the intake manifold 14, an air cleaner (not shown), a compressor 18 constituting a turbocharger 17, and an intercooler 19 are provided in order from the upstream side. The exhaust passage 20 connected to the exhaust manifold 15 is provided with a turbine 22 that is connected to the compressor 18 via a connecting shaft and constitutes the turbocharger 17.

  The EGR device 25 includes an EGR passage 26 that connects the exhaust manifold 15 and the intake passage 16 and introduces a part of the exhaust gas into the intake passage 16 as EGR gas. The EGR device 25 includes, in the EGR passage 26, a water-cooled EGR cooler 27 that cools EGR gas using a liquid as a refrigerant, and an EGR valve 28 that changes the flow path cross-sectional area of the EGR passage 26. The opening degree of the EGR valve 28 is controlled by an EGR control device (not shown).

The EGR cooler 27 will be described with reference to FIG.
As shown in FIG. 2, the EGR cooler 27 is a multitubular heat exchanger. The EGR cooler 27 includes a cylindrical body 31, an inlet cover 32 connected to one end of the body 31, an outlet cover 33 connected to the other end of the body 31, and a multi-tube located inside the body 31. A cooling unit 34 of the type. The body 31, the inlet cover 32, and the outlet cover 33 are made of stainless steel. The EGR cooler 27 is mounted on the vehicle such that the extending direction of each cooling pipe 35 is substantially along the horizontal direction.

  The cooling unit 34 includes a plurality of cooling pipes 35 through which EGR gas circulates, stainless steel partition plates 36 and 37 that support the plurality of cooling pipes 35 and partition the space in the body 31, and cooling water in the body 31. Baffle plate 38 that forms a flow. One end portion of each cooling pipe 35 is inserted into a plurality of insertion holes 36a of the partition plate 36, and is supported by the partition plate 36 in a state where a gap between the insertion hole 36a and the partition plate 36 is sealed. The other end of each cooling pipe 35 is inserted into a plurality of insertion holes 37a included in the partition plate 37, and is supported by the partition plate 37 in a state where a gap between the insertion hole 37a and the partition plate 37 is sealed. Some cooling pipes 35 are supported by the baffle plate 38 by being individually inserted into a plurality of insertion holes 38 a included in the baffle plate 38 in which a lower portion in the vertical direction is cut out. A gap between the peripheral portion of the partition plate 36 and the peripheral portion of the partition plate 37 is sealed with the body 31. At least one of the partition plate 36 and the partition plate 37 is fixed to the body 31. In the EGR cooler 27, the internal space of each cooling pipe 35, the space surrounded by the partition plate 36 and the inlet cover 32, the space surrounded by the partition plate 37 and the outlet cover 33, these spaces are EGR gas distribution spaces. is there.

  In the body 31, a space between the partition plate 37 and the baffle plate 38 is a first cooling water channel 40, and a space between the baffle plate 38 and the partition plate 36 is a second cooling water channel 42, and the baffle plate 38. A gap between the baffle plate 38 and the body 31 formed by the notch is a communication path 43. Cooling water flows into the first cooling water channel 40 from an inflow portion 44 formed in the body 31. Thereafter, the cooling water flows into the second cooling water passage 42 through the communication passage 43 and flows out of the body 31 from the outflow portion 45 formed in the body 31.

  In the EGR cooler 27 having such a configuration, the EGR gas flows into the EGR cooler 27 from the inlet 32 a of the inlet cover 32, and after heat exchange with the cooling water is performed in the cooling unit 34, the EGR cooler is passed through the outlet 33 a of the outlet cover 33. 27 flows out.

  The cooling unit 34 includes a first cooling element 47 including a plurality of first cooling pipes 46 and a second cooling element 49 including a plurality of second cooling pipes 48 having higher corrosion resistance than the first cooling pipe 46. The first cooling element 47 is composed of a cooling pipe 35 that can face the first cooling pipe 46 constituting the first cooling element 47 in the horizontal direction in a state where the EGR cooler 27 is mounted on the vehicle. It is a cooling part. The first cooling element 47 of the present embodiment is composed of only a plurality of first cooling pipes 46. The second cooling element 49 is located in a lower region in the vertical direction than the first cooling element 47 in a state where the EGR cooler 27 is mounted on the vehicle.

  The first cooling pipe 46 is a stainless steel spiral tube. The spiral tube is a tube in which fins extending spirally in the extending direction of the cooling pipe are formed on at least one of the outer peripheral surface and the inner peripheral surface of the cooling pipe. The first cooling pipe 46 of the present embodiment has fins on both the outer peripheral surface and the inner peripheral surface. The thickness of the spiral tube is the thickness of the thinnest portion in the portion where the spiral fin is formed. On the other hand, the second cooling pipe 48 is a straight tube made of stainless steel. A straight tube is a tube in which an annular cross-sectional shape continues along the extending direction of the tube.

  An example of a combination of the material of the first cooling pipe 46 and the material of the second cooling pipe 48 is shown in Table 1. The first cooling pipe 46 and the second cooling pipe 48 are not limited to those selected from the materials shown in Table 1 as long as the second cooling pipe 48 has better corrosion resistance than the first cooling pipe 46. Absent.

  In Table 1, NAS254N and NAS354N are product names of Nippon Yakin Kogyo Co., Ltd., NSSC270 is a product name of Nippon Steel & Sumikin Stainless Steel Co., Ltd., and NSSSC-NAR-HCR-18 is a product of Nippon Steel & Sumikin Co., Ltd. Name.

In addition, Table 2 shows chemical components of the respective materials described in Table 1.

  Table 3 shows the results of corrosion tests performed on the materials shown in Table 1. In this corrosion test, the sample was immersed in sulfuric acid having a predetermined concentration for a predetermined time, and the difference between the weight before immersion and the weight after immersion was set as the corrosion amount. In Table 3, the test result is shown by the sulfuric acid corrosive magnification which is the ratio of the corrosion amount to SUS316L.

The operation of the above-described EGR cooler 27 will be described.
The temperature of the EGR gas remaining in the EGR cooler when the engine 10 is stopped is more likely to decrease as the EGR gas is closer to the cooling pipe 35. Due to such a decrease in the temperature of the EGR gas, convection of the EGR gas occurs in the EGR gas circulation space. Therefore, the condensate is more easily generated in the second cooling element 49 than in the first cooling element 47 during the stop period of the engine 10. That is, the condensate is easily generated in the second cooling pipe 48 having higher corrosion resistance than the first cooling pipe 46. As a result, the corrosion of the cooling pipe 35 during the stop period of the engine 10 is suppressed as compared with the case where the cooling unit 34 is configured by only the first cooling pipe 46.

  In addition, the material cost concerning the EGR cooler 27 has a large proportion of the cooling pipe 35. Moreover, the cooling pipe 35 with high corrosion resistance is obtained and expensive. Therefore, in order to suppress the material cost of the EGR cooler 27 while suppressing the corrosion of the cooling pipe during the engine stop period, the number of the second cooling pipes 48 constituting the second cooling element 49 with respect to the total number of the cooling pipes 35. The ratio is preferably ½ or less, more preferably ３ or less. In consideration of the material cost of the cooling pipe, it is preferable that the first cooling pipe 46 is SUS304 or SUS304L and the second cooling pipe 48 is SUS316L.

According to the EGR cooler 27 of the above embodiment, the effects listed below are obtained.
(1) Since condensed water is easily generated in the second cooling pipe 48, corrosion of the cooling pipe 35 during the stop period of the engine 10 is suppressed.

  (2) Since a part of the cooling pipe 35 constituting the cooling part 34 is the second cooling pipe 48, the material of the EGR cooler 27 is compared with the case where the cooling part 34 is constituted only by the second cooling pipe 48. Costs can be reduced.

  (3) The cooling unit 34 includes one first cooling element 47 and one second cooling element 49, and the first cooling element 47 includes a plurality of first cooling pipes 46. As a result, there are only two types of cooling pipes 35, the first cooling pipe 46 and the second cooling pipe 48.

  (4) Since the ratio of the number of the second cooling pipes 48 to the total number of the cooling pipes 35 is 1/2 or less, the material of the EGR cooler 27 is suppressed while suppressing the corrosion of the cooling pipes 35 during the stop period of the engine 10. Costs can be reduced.

(5) Since the ratio of the number of the second cooling pipes 48 to the total number of the cooling pipes 35 is 1/3 or less, the material cost of the EGR cooler 27 is further suppressed.
(6) Since the first cooling element 47 includes the plurality of first cooling pipes 46, the material cost of the EGR cooler 27 can be reduced as compared with the case where the first cooling element 47 includes the second cooling pipe 48.

(7) Since the first cooling pipe 46 is a spiral tube, the cooling efficiency of the EGR cooler 27 is improved.
(8) Since the 2nd cooling pipe 48 is a straight tube, when the 1st cooling pipe 46 and the 2nd cooling pipe 48 have the same outer diameter, the freedom degree regarding the thickness of the 2nd cooling pipe 48, for example. Will improve.

In addition, the said embodiment can also be suitably changed and implemented as follows.
Each of the first cooling pipe 46 and the second cooling pipe 48 may be a spiral tube or a straight tube.

  -In the EGR cooler 27, the number of the 1st cooling pipes 46 which comprise the 1st cooling element 47, and the number of the 2nd cooling pipes 48 which comprise the 2nd cooling element 49 change according to the design matter at that time. Is possible.

The second cooling element 49 may be one second cooling pipe 48.
The first cooling element 47 includes a cooling pipe 35 that can be opposed to any one of the first cooling pipes 46 constituting the first cooling element 47 in the horizontal direction in a state where the EGR cooler 27 is mounted on the vehicle. It is a cooling part. Therefore, the first cooling element 47 may include a second cooling pipe 48 that can face the first cooling pipe 46 in the horizontal direction in a state where the EGR cooler 27 is mounted on the vehicle.

  The EGR cooler 27 includes, for example, a third cooling pipe having a higher corrosion resistance than the second cooling pipe 48 in addition to the first cooling element 47 and the second cooling element 49, and is more vertically oriented than the second cooling element 49. The 3rd cooling part located in the lower side in may be provided. According to such a configuration, corrosion of the cooling pipe during the stop period of the engine 10 is further suppressed.

  The EGR cooler 27 is not limited to a liquid water-cooled refrigerant, but may be an air-cooled refrigerant that is air. In addition, the EGR cooler 27 is folded back on the outlet cover 33 side after the EGR gas flowing in from the inlet cover 32 side passes through the second cooling element 49, passes through the first cooling element 47, and returns to the inlet cover 32 side again. A so-called two-pass heat exchanger may be used. At this time, by setting the second cooling element 49 upstream, the condensate is easily generated in the second cooling element 49 even during the drive period of the engine 10.

The EGR cooler 27 may be configured such that the refrigerant passes through each cooling pipe 35 and the EGR gas passes through the body 31. Even if it is such a structure, the effect mentioned above is acquired.
The engine 10 may be a diesel engine or a gasoline engine.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 11 ... Cylinder block, 12 ... Cylinder, 14 ... Intake manifold, 15 ... Exhaust manifold, 16 ... Intake passage, 17 ... Turbocharger, 18 ... Compressor, 19 ... Intercooler, 20 ... Exhaust passage, 22 ... Turbine, 25 ... EGR device, 26 ... EGR passage, 27 ... EGR cooler, 28 ... EGR valve, 31 ... fuselage, 32 ... inlet cover, 32a ... inlet, 33 ... outlet cover, 33a ... outlet, 34 ... cooling section, 35 ... cooling Pipe, 36 ... Partition plate, 36a ... Insertion hole, 37 ... Partition plate, 37a ... Insertion hole, 38 ... Baffle plate, 38a ... Insertion hole, 40 ... First cooling water channel, 42 ... Second cooling water channel, 43 ... Communication channel , 44 ... inflow part, 45 ... outflow part, 46 ... first cooling pipe, 47 ... first cooling element, 48 ... second cooling pipe, 49 ... second cooling element

Claims (5)

Provided with a multi-tube cooling section composed of a plurality of cooling pipes,
The cooling unit is
A first cooling element including a first cooling pipe;
A second cooling element having a corrosion resistance higher than that of the first cooling pipe, and a second cooling element positioned below the first cooling element in the vertical direction when the EGR cooler is mounted on a vehicle. EGR cooler. The EGR cooler according to claim 1, wherein the plurality of cooling pipes are configured by the first cooling pipe and the second cooling pipe. The EGR cooler according to claim 2, wherein the first cooling element includes the first cooling pipe. The EGR cooler according to claim 2 or 3, wherein a ratio of the number of the second cooling pipes constituting the second cooling element to a total number of the cooling pipes included in the cooling unit is 1/2 or less. The first cooling pipe is a spiral tube;
The EGR cooler according to any one of claims 1 to 4, wherein the second cooling pipe is a straight tube.

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