JP4407666B2 - Exhaust heat exchanger - Google Patents

Description

  The present invention relates to an exhaust system heat exchanger for recovering exhaust heat by performing heat exchange between an exhaust gas of an automobile or the like and a coolant.

An inner pipe and an outer pipe, which have an exhaust control valve arranged on the upstream side, form a double pipe structure. An exhaust cooling device for a mounted engine is known (see, for example, Patent Document 1).
JP 2004-293395 A

  However, in the conventional technology as described above, when the engine is stopped, the circulation of the cooling water is stopped in the cooling water passage in the exhaust cooler. I am worried about it.

  In view of the above fact, an object of the present invention is to obtain an exhaust system heat exchanger that can prevent the cooling medium in the shell from becoming high temperature.

  An exhaust system heat exchanger according to the first aspect of the present invention includes an exhaust gas passage for circulating an exhaust gas, and a cooling medium passage provided adjacent to the exhaust gas passage for circulating a cooling medium. A shell formed inside, a first communication channel portion that communicates an upper portion in the gravity direction on one end side in the flow direction of the cooling medium with the outside of the shell, and the cooling medium channel. A second communication channel portion that communicates the lower part of the gravity direction on the other end side in the flow direction of the cooling medium and the outside of the shell, and a portion of the second communication channel unit that is located in the shell is exhausted. And a heat insulating part that insulates the gas.

  In the exhaust system heat exchanger according to the first aspect, heat exchange is performed between the exhaust gas flowing through the exhaust gas flow path and the cooling medium flowing through the cooling medium flow path in the shell. The cooling medium flows through the cooling medium flow path from the first communication flow path section toward the second communication flow path section or from the second communication flow path section toward the first communication flow path section, and circulates inside and outside the shell. (Forced circulation). At this time, in the 2nd communicating channel part thermally insulated by the heat insulation part, the temperature (rise) of a cooling medium is suppressed lower than the temperature of the cooling medium in a cooling medium channel.

  When the forced circulation of the cooling medium is stopped, the cooling medium in the second communication flow path portion having a specific gravity larger than that of the cooling medium in the cooling medium flow path due to the relatively low temperature causes a downward flow due to gravity. It occurs and flows into the lower part in the direction of gravity on the other end side of the cooling medium flow direction in the cooling medium flow direction. As a result, natural convection of the cooling medium toward the first communication flow path portion side occurs in the cooling medium flow path, and the cooling medium is prevented from reaching a high temperature. In addition, by providing the heat insulating portion, a portion (second communication flow path portion) in which a part of the cooling medium is relatively low temperature can be provided in the shell in order to cause natural convection. Thereby, the 2nd communication channel part is covered and protected by the shell.

  Thus, in the exhaust system heat exchanger according to the first aspect, the cooling medium in the shell can be prevented from becoming high temperature.

  An exhaust system heat exchanger according to a second aspect of the present invention is the exhaust system heat exchanger according to the first aspect, wherein a portion of the second communication flow path portion excluding the through portion of the shell is a flow of the exhaust gas. The whole is formed so as to overlap the cooling medium flow path when viewed from the direction.

  The exhaust system heat exchanger according to claim 2, wherein the second communication portion overlapping with the cooling medium flow passage as a whole except the through portion of the shell as seen from the exhaust gas flow direction obstructs the flow of the exhaust gas. As a result, an increase in exhaust gas back pressure is suppressed.

  An exhaust system heat exchanger according to a third aspect of the present invention is the exhaust system heat exchanger according to the second aspect, wherein the portion of the second communication flow path portion excluding the through portion of the shell is the flow of the exhaust gas. It has the same cross-sectional shape as the cooling medium flow path when viewed from the direction.

  In the exhaust system heat exchanger according to claim 3, the second communication flow portion that overlaps the cooling medium flow passage as a whole except for the through portion of the shell as viewed from the exhaust gas flow direction has the above-described back pressure increase. A low-temperature cooling medium for generating natural convection can be stored while maintaining the suppression effect.

  An exhaust system heat exchanger according to a fourth aspect of the present invention is the exhaust system heat exchanger according to the second or third aspect, wherein the cooling medium passage coaxially surrounds the exhaust gas passage. Is made.

  In the exhaust system heat exchanger according to claim 4, for example, a cooling medium flow path between an inner cylinder wall defining an exhaust gas flow path and an outer cylinder wall provided coaxially on the outer side of the inner cylinder wall. Is formed, and the second communication flow path portion is provided on either side of the axial direction with respect to the cooling medium flow path. When the forced circulation is stopped, the low-temperature cooling medium from the second communication channel flows into the lower part of the second communication channel that is continuous in a cylindrical shape, so that a stagnation part of the flow of the cooling medium due to natural convection hardly occurs. It is possible to effectively prevent the cooling medium in the shell from becoming high temperature.

  An exhaust system heat exchanger according to a fifth aspect of the present invention is the exhaust system heat exchanger according to any one of the second to fourth aspects, wherein the second communication flow path portion is the cooling medium flow path. The exhaust gas is disposed downstream of the exhaust gas in the flow direction.

  In the exhaust system heat exchanger according to claim 5, the exhaust gas that has been absorbed by heat exchange with the cooling medium comes into contact with the second communication flow path portion, so that the exhaust gas is received from the exhaust gas in the second communication flow path portion. The amount of heat is reduced. For this reason, the temperature of the cooling medium in the second communication channel can be lowered.

  The exhaust system heat exchanger according to the invention described in claim 6 is the exhaust system heat exchanger according to any one of claims 1 to 5, wherein the second communication channel is in the cooling water channel. The other end in the flow direction of the cooling medium is partitioned by a partition plate.

  In the exhaust system heat exchanger according to claim 6, since the cooling medium flow path and the second communication flow path portion are integrally formed, in other words, the cooling medium flow path and the second communication flow path portion Since there is no space through which the exhaust gas flows, the contact area of the second communication channel with the exhaust gas is small, and the temperature of the cooling medium in the second communication channel can be lowered.

  As described above, the exhaust system heat exchanger according to the present invention has an excellent effect that the cooling medium in the shell can be prevented from becoming a high temperature.

  An exhaust system heat exchanger 10 according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. In the following description, when the terms upstream and downstream are simply used, they indicate upstream and downstream in the flow direction of the exhaust gas. In addition, an arrow UP and an arrow LO shown in each figure indicate an upper side and a lower side in the direction of gravity (the vehicle body vertical direction), respectively.

  FIG. 2 shows a schematic overall flow diagram of the exhaust heat recovery system 18 to which the exhaust heat exchanger 10 is applied. As shown in this figure, the exhaust heat recovery system 18 recovers the heat of the exhaust gas of the internal combustion engine 12 of the automobile by heat exchange with the engine cooling water, and uses it for heating, promoting warm-up of the engine 12 or the like. Device.

  The engine 12 is connected to an exhaust pipe 14 that constitutes an exhaust path for leading exhaust gas. A catalytic converter 16, an exhaust system heat exchanger 10, and a main muffler 20 are disposed in this order from the upstream side on the exhaust gas discharge path by the exhaust pipe 14. The catalytic converter 16 is configured to purify exhaust gas passing therethrough by a built-in catalyst 16A. The main muffler 20 as a silencer is configured to reduce the exhaust noise generated when exhaust gas is discharged into the atmosphere.

  The exhaust system heat exchanger 10 is configured to recover the heat of the exhaust gas to the engine coolant by heat exchange between the exhaust gas and the engine coolant. Further, in this exhaust system heat exchanger 10, an exhaust gas bypass channel 22 and a channel switching valve 24 as a channel switching device for opening and closing the bypass channel 22 are disposed. The exhaust heat recovery mode in which the gas exchanges heat with the engine coolant and the normal mode in which the exhaust gas passes through the bypass channel 22 can be switched. This will be specifically described below.

  As shown in FIGS. 1 (A) and 1 (B), the exhaust system heat exchanger 10 includes an inner cylinder 26 and a outer cylinder 28 as a shell, which are each formed in a cylindrical shape and arranged concentrically. A heat exchanging unit 30 for exchanging heat between the exhaust gas and the engine coolant is configured between the inner cylinder 26 and the outer cylinder 28.

  The inner cylinder 26 is disposed so that the axial direction coincides with the horizontal direction (for example, the longitudinal direction of the vehicle body), passes through the axial center portion of the outer cylinder 28, and both ends in the axial direction are connected to the exhaust pipe 14. Are continuous. The inner cylinder 26 may be configured as a part of the exhaust pipe 14. Further, the exhaust system heat exchanger 10 includes a conical cylinder 32 whose upstream end is fixed to the outer periphery of the inner cylinder 26 in an airtight state and whose downstream end is connected to the upstream end 28A of the outer cylinder 28, and whose downstream end is the inner cylinder. 26 and a conical cylinder 34 that is fixed in an airtight manner to the outer periphery of the outer cylinder 26 and that has an upstream end connected to the downstream end 28B of the outer cylinder 28.

  The heat exchanger 30 in the exhaust heat exchanger 10 is formed between an exhaust gas inlet header 36, which is a space between the inner cylinder 26 and the conical cylinder 32, and the inner cylinder 26 and the outer cylinder 28. An exhaust gas heat exchange path 38 that is a cylindrical space and an exhaust gas outlet header 40 that is a space between the inner cylinder 26 and the conical cylinder 34 are formed. On the other hand, the inside of the inner cylinder 26 is the bypass channel 22 described above. The inner cylinder 26 is provided in an inner portion of the conical cylinder 32 and communicates with an exhaust gas inlet header 36, and is provided in an inner portion of the conical cylinder 34 and communicates with an exhaust gas outlet header 40. The heat exchanger outlet hole 26B is formed.

  A cooling water pipe 42 is disposed in the exhaust gas heat exchange path 38 to constitute a cooling water heat exchange path 44 that is a flow path of engine cooling water in the exhaust heat exchanger 10. In this embodiment, the cooling water pipe 42 forms a cylindrical cooling water heat exchange path 44 inside the double cylinder. A cooling water inlet pipe 46 serving as a first communication channel is connected to the cooling water pipe 42 upstream of the cooling water flow direction (forced circulation direction). The cooling water inlet pipe 46 penetrates the outer cylinder 28 and has a cooling water inlet 44A positioned at the uppermost part in the gravity direction in the cylindrical cooling water heat exchange path 44 that is axially aligned with the horizontal direction, and the outer cylinder. 28 communicates with the outside (heater hot water passage 60 described later).

  On the other hand, on the downstream side of the cooling water flow direction (forced circulation direction) in the cooling water pipe 42, a cooling water outlet 44B that opens toward the downstream side in the exhaust gas flow direction is formed at the lowest part in the gravity direction. A cooling water outlet pipe 48 serving as a second communication channel is connected to the cooling water outlet 44B. The cooling water outlet pipe 48 is formed in an annular shape whose inner and outer diameters match the inner and outer diameters of the cooling water pipe 42, and is coaxially disposed on the downstream side of the cooling water pipe 42 in the exhaust gas flow direction. An outlet port portion 52 that penetrates the tube 28 and communicates the uppermost portion in the gravity direction of the ring pipe 50 and the outside of the outer tube 28 is configured. Therefore, the cooling water outlet 44 </ b> B of the cooling water heat exchange path 44 communicates with the outside of the outer cylinder 28 via the cooling water outlet pipe 48.

  The ring pipe 50 having the above configuration overlaps with the cooling water pipe 42 so that the whole is hidden behind the cooling water pipe 42 (there is no projected portion) when viewed from the upstream side in the exhaust gas flow direction. ing. In this embodiment, the ring pipe 50 is located near the boundary between the exhaust gas heat exchange path 38 and the exhaust gas outlet header 40, and is slightly separated from the downstream end of the cooling water pipe 42.

  The cooling water outlet pipe 48 has a heat insulating structure provided with a heat insulating material 54 as a heat insulating portion. The heat insulating material 54 is provided on the inner surfaces of the ring pipe 50 and the outlet port portion 52 constituting the cooling water outlet pipe 48 over substantially the entire circumference, and insulates the inside of the cooling water outlet pipe 48 from the exhaust gas. Yes. The heat insulating material 54 may be provided on the outer surface (both inner and outer surfaces) of the cooling water outlet pipe 48, but it is desirable that the outer shape overlaps the cooling water pipe 42 as a whole. As the heat insulating material 54, for example, silicon, heat resistant resin, glass wool or ceramic wool held by an iron plate or the like is used.

  In the exhaust system heat exchanger 10 described above, when the flow path switching valve 24 closes the inner cylinder 26 (bypass flow path 22), the exhaust gas flows through the exhaust gas heat exchange path 38 to exchange heat. In the case where the function is achieved and the flow path switching valve 24 opens the inner cylinder 26, the exhaust gas mainly flows through the bypass flow path 22 to perform the exhaust gas bypass function. Note that the flow resistance (pressure loss) of the exhaust gas heat exchange path 38 provided with the cooling water pipe 42 is larger than the flow resistance of the opened bypass flow path 22, and the flow path switching valve 24 connects the inner cylinder 26. When it is open, almost no exhaust gas flows through the exhaust gas heat exchange path 38.

  The flow path switching valve 24 is controlled by an ECU as a control device (not shown). For example, when a warm-up promotion request is made for the engine 12, a heating request is made when the engine coolant temperature is low, etc. 22 is closed.

  On the other hand, the exhaust heat recovery system 18 includes a front heater core 56 and a rear heater core 58 that recover heat of the engine cooling water for heating, and a heater hot water passage 60 that circulates the engine cooling water to the front heater core 56 and the rear heater core 58. Yes. The front heater core 56 and the rear heater core 58 are arranged in parallel. And the exhaust system heat exchanger 10 is arrange | positioned in the heater warm water path 60 in the downstream of the rear heater core 58. FIG. That is, the cooling water inlet pipe 46 is disposed on the heater warm water channel 60 on the rear heater core 58 side, and the outlet port portion 52 of the cooling water outlet pipe 48 is disposed on the upstream side of the engine 12 in the heater warm water channel 60. In this embodiment, the exhaust system heat exchanger 10 is arranged in parallel to the front heater core 56 and in series to the rear heater core 58 in the engine coolant system.

  Therefore, in the exhaust heat recovery system 18, the engine coolant flows as indicated by the arrows on the heater hot water passage 60 in FIG. As a result, hot hot water that has passed through the engine 12 is heat-exchanged when passing through the front heater core 56 and the rear heater core 58 and used for heating, and the engine cooling water that has been cooled by the rear heater core 58 is used as the exhaust system heat exchanger 10. The heat exchange with the exhaust gas is introduced. The engine coolant that has passed through the exhaust system heat exchanger 10 is returned to the engine 12 together with the engine coolant that has passed through the front heater core 56. Thus, the exhaust system heat exchanger 10 is configured to function as a preheater that preheats the engine coolant before being heated by the engine 12 from the viewpoint of the heating function, for example.

  Next, the operation of the first embodiment will be described.

  In the exhaust heat recovery system 18 configured as described above, when the engine coolant temperature is low, such as immediately after the engine 12 is started, the ECU closes the flow path switching valve 24 based on, for example, a heating request or a warm-up promotion request for the engine 12. Driven to close the bypass passage 22. That is, the exhaust heat recovery mode is selected. Then, the exhaust gas of the engine 12 does not flow through the bypass flow path 22 but is introduced into the exhaust gas heat exchange path 38 of the exhaust system heat exchanger 10. The exhaust gas introduced into the exhaust gas heat exchange path 38 exchanges heat with the engine coolant in the exhaust system heat exchanger 10 to heat the engine coolant. Thereby, heating is accelerated | stimulated or the warming-up of the engine 12 is accelerated | stimulated.

  On the other hand, when the engine coolant temperature rises and exceeds the threshold value, the ECU opens the flow path switching valve 24 to open 22. That is, the exhaust heat recovery mode is switched to the normal mode. Then, the exhaust gas mainly circulates in the bypass flow path 22. Even in this case, the engine cooling water circulates in the heater hot water passage 60 including the cooling water pipe 42 by the operation of the engine 12, that is, the water pump.

  When the engine 12 is stopped, the operation of the water pump is stopped, so that the forced circulation of the engine cooling water by the water pump is stopped. On the other hand, the inner cylinder 26 (bypass passage 22) of the exhaust system heat exchanger 10 is maintained at a high temperature for a while after the engine 12 is stopped. Heat is transferred from the high temperature bypass passage 22 to the engine coolant in the coolant pipe 42.

  Here, in the exhaust system heat exchanger 10, since the heat insulating material 54 is provided in the cooling water outlet pipe 48, the engine cooling water temperature in the cooling water outlet pipe 48 in which the amount of heat received from the exhaust gas is relatively small is the cooling water heat. Compared to the engine coolant temperature in the exchange path 44, the temperature is low and the specific gravity is large. Therefore, the engine cooling water in the cooling water outlet pipe 48 generates a downward flow in the gravitational direction due to gravity, and flows from the cooling water outlet 44 </ b> B to the lowermost portion at one end in the longitudinal direction of the cooling water heat exchange path 44. Thereby, the engine cooling water in the cooling water heat exchange path 44 is pushed out, and a flow toward the cooling water inlet 44A is generated macroscopically. That is, natural convection of engine coolant occurs in the exhaust system heat exchanger 10 (outer cylinder 28).

  In this way, natural convection of the engine cooling water, that is, circulation flow is generated when the engine 12 is stopped, so that the engine cooling water is prevented from excessively rising in temperature or boiling. In particular, the exhaust system heat exchanger 10 has a large exhaust gas capacity due to the bypass passage 22 being arranged at the center, and the engine coolant tends to become hot when the engine 12 is stopped. 50) and the heat insulating material 54 can prevent the cooling medium of the cooling water pipe 42 from becoming high temperature.

  Further, in the exhaust system heat exchanger 10, electric power is not generated unlike the configuration in which a forced circulation flow of engine cooling water is generated when the engine 12 is stopped using, for example, an electric pump. It is possible to prevent the fuel consumption from deteriorating while preventing the temperature from rising or boiling.

  Furthermore, in the exhaust system heat exchanger 10, the ring pipe 50 has substantially the same cross-sectional shape as the cooling water pipe 42 as viewed from the exhaust gas flow direction and is hidden behind the cooling water pipe 42. Does not obstruct gas flow. Therefore, it is possible to prevent the back pressure of the exhaust gas flow from being increased by providing the cooling water outlet pipe 48 including the ring pipe 50. Further, since the cross-sectional shape of the ring pipe 50 substantially matches the cross-sectional shape of the cooling water heat exchange path 44, it is possible to increase the amount of low-temperature engine cooling water retained while maintaining the above-described back pressure increase suppressing effect.

  And in the exhaust system heat exchanger 10, since the cooling water heat exchange path 44 is formed in a cylindrical shape, in other words, it is continuous in the circulation direction while maintaining a required surface area (in this embodiment, a single ) Since the cooling water flow path is configured, stagnation of engine cooling water is unlikely to occur due to natural convection, and it is possible to effectively prevent the cooling medium in the heat exchange unit 30 (outer cylinder 28) from becoming high temperature. .

  In addition, in the exhaust heat exchanger 10, the ring pipe 50 is located downstream in the exhaust gas flow direction with respect to the cooling water pipe 42, so that the amount of heat received from the exhaust gas in the ring pipe 50 is reduced. For this reason, the engine coolant temperature in the ring pipe 50 can be lowered. Thereby, the natural convection at the time of the stop of the engine 12 can be promoted.

  Here, in the exhaust heat exchanger 10, it is realized that the specific gravity of the engine cooling water in the ring pipe 50 disposed in the outer cylinder 28 is relatively increased by providing the heat insulating material 54. . As a result, in order to generate natural convection of the engine cooling water, a part of the engine cooling water flow path is disposed outside the outer cylinder 28 on the side of the cooling water pipe 42, so that it can be removed by a stepping stone or the like during vehicle travel. Damage is prevented. That is, the ring pipe 50 is protected by the outer cylinder 28.

  Next, an exhaust system heat exchanger 70 according to a second embodiment of the present invention will be described with reference to FIG. Note that parts and portions that are basically the same as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof is omitted.

  3A shows a cross-sectional view of the exhaust system heat exchanger 70, and FIG. 3B shows a cross-sectional view taken along line 3B-3B of FIG. 3A. . As shown in these drawings, the exhaust system heat exchanger 70 has a ring shape in which the cooling water outlet pipe 48 is provided integrally with the cooling water pipe 42 in place of the ring pipe 50 which is a separate body from the cooling water pipe 42. The exhaust system heat exchanger 10 according to the first embodiment is different from the exhaust system heat exchanger 10 in that the pipe line 72 is provided.

  Specifically, the ring-shaped pipe line 72 has an engine cooling water path (second communication flow path) partitioned from the cooling water heat exchange path 44 by interposing a partition plate 74 on the downstream end side of the cooling water pipe 42. Part). The partition plate 74 is formed such that the lowermost portion of the ring-shaped flat plate corresponding to the cross-sectional shape of the cooling water heat exchange path 44 (cooling water pipe 42) is cut along the horizontal plane, and further upward from the uppermost portion of the ring-shaped portion. The extended portion enters the outlet port portion 52. Thereby, the ring-shaped pipe line 72 and the cooling water heat exchange path 44 communicate with each other at the cooling water outlet 44 </ b> B formed by forming the cut portion in the partition plate 74.

  The ring-shaped pipeline 72 formed in this way is provided with a heat insulating material 54 as with the ring pipe 50. Other configurations of the exhaust system heat exchanger 70 are the same as the corresponding configurations of the exhaust system heat exchanger 10.

  Therefore, the exhaust system heat exchanger 70 according to the second embodiment can obtain the same effect by the same operation as the exhaust system heat exchanger 10 according to the first embodiment. Further, in the exhaust system heat exchanger 70, the ring-shaped pipe line 72 is formed integrally with the cooling water pipe 42, so that the exhaust gas is interposed between the cooling water pipe 42 and the ring pipe 50 like the exhaust system heat exchanger 10. Is not formed, and the contact area of the ring-shaped pipe line 72 with the exhaust gas is small. For this reason, the amount of heat received from the exhaust gas in the ring-shaped pipeline 72 is further reduced, and the engine coolant in the ring-shaped pipeline 72 can be kept at a lower temperature.

  In each of the above embodiments, the cooling water inlet pipe 46 is an engine cooling water inlet in a forced circulation flow, and the cooling water outlet pipe 48 is an outlet (a parallel flow heat exchanger). The present invention is not limited to this. For example, engine cooling water may be introduced from the outlet port portion 52 of the cooling water outlet pipe 48 and discharged from the cooling water inlet pipe 46 in forced circulation.

  Moreover, in each above-mentioned embodiment, although the cooling water heat exchange path 44 was formed with the single cooling water pipe 42, this invention is not limited to this, For example, the cooling water heat exchange path 44 is shown. May form a plurality of concentric cylindrical layers, and the cooling water heat exchange path 44 may be constituted by a plurality of straight pipes.

  Furthermore, in the said embodiment, although the bypass flow path 22 showed the example formed in the inner cylinder 26 which comprises the exhaust system heat exchanger 10, this invention is not limited to this, For example, the bypass flow path 22 May be constituted by a pipe arranged in parallel to the side of the exhaust system heat exchanger 10, or the present invention may be applied to a configuration without the bypass flow path 22.

It is a figure which shows the exhaust system heat exchanger which concerns on the 1st Embodiment of this invention, Comprising: (A) is a sectional side view, (B) is sectional drawing along the 1B-1B line | wire of FIG. 1 (A). is there. 1 is a system flow diagram of an exhaust heat recovery system to which an exhaust system heat exchanger according to a first embodiment of the present invention is applied. It is a figure which shows the exhaust system heat exchanger which concerns on the 2nd Embodiment of this invention, Comprising: (A) is a sectional side view, (B) is sectional drawing along the 3B-3B line | wire of FIG. 3 (A). is there.

Explanation of symbols

10 Exhaust system heat exchanger 28 Outer cylinder (shell)
38 Exhaust gas heat exchange path (exhaust gas path)
44 Cooling water heat exchange path (cooling medium flow path)
46 Cooling water inlet pipe (first communication channel)
48 Cooling water outlet pipe (second communication channel)
50 Ring pipe (excluding the part where the shell penetrates in the second communication channel)
52 Outlet port part (through portion of shell in second communication flow path part)
54 Heat insulation material (heat insulation part)
70 Exhaust system heat exchanger 72 Ring-shaped pipeline (portion excluding shell penetration in second communication channel)
74 Partition plate

Claims (6)

A shell in which an exhaust gas flow path for circulating the exhaust gas and a cooling medium flow path provided adjacent to the exhaust gas flow path for circulating the cooling medium are formed;
A first communication channel portion that communicates the upper part of the gravity direction on one end side of the cooling medium channel in the flow direction of the cooling medium and the outside of the shell;
A second communication channel portion that communicates the lower part of the gravity direction on the other end side in the flow direction of the cooling medium with the outside of the shell;
A heat insulating part that insulates the exhaust gas from a portion located in the shell in the second communication flow path part;
Exhaust system heat exchanger with   2. The exhaust gas according to claim 1, wherein a portion of the second communication flow path portion excluding the through portion of the shell is formed so as to entirely overlap the cooling medium flow path when viewed in the flow direction of the exhaust gas. System heat exchanger.   3. The exhaust system heat exchanger according to claim 2, wherein a portion of the second communication flow path portion excluding the through portion of the shell has the same cross-sectional shape as the cooling medium flow path when viewed from the flow direction of the exhaust gas.   The exhaust system heat exchanger according to claim 2 or 3, wherein the cooling medium flow path has a cylindrical shape that coaxially surrounds the exhaust gas flow path.   The exhaust system heat exchanger according to any one of claims 2 to 4, wherein the second communication flow path portion is disposed on the downstream side in the flow direction of the exhaust gas with respect to the cooling medium flow path.   The exhaust system according to any one of claims 1 to 5, wherein the second communication channel is formed by partitioning the other end of the coolant flow direction in the cooling water channel with a partition plate. Heat exchanger.

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