JP2015010471A - Exhaust gas cooling system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas cooling system for an internal combustion engine having an exhaust gas cooling structure, the system materializing suitable suppression of a reduction in the temperature of exhaust gas during low-load operation of the internal combustion engine.SOLUTION: There is provided the exhaust gas cooling system for the internal combustion engine having exhaust branch pipes respectively connected to a plurality of exhaust ports formed in cylinder heads in association with a plurality of cylinders, and an exhaust emission control catalyst arranged in an exhaust pipe positioned downstream of a collected part of the exhaust branch pipes. The exhaust gas cooling system includes a cooling part for cooling the exhaust branch pipes or the exhaust ports, and a heat transfer inhibiting part for inhibiting heat transmission from the exhaust branch pipes downstream of positions to be cooled by the cooling part to the cooling part, the heat transfer inhibiting part having heat transmission inhibiting capability set in such a manner that the higher inhibiting capability is given to the exhaust port from which higher temperature exhaust gas is exhausted toward the exhaust branch pipe when the internal combustion engine is in a predetermined low-load operating condition.

Description

  The present invention relates to an exhaust cooling system for an internal combustion engine.

  A technique for cooling the exhaust gas is known in order to avoid deterioration of the exhaust purification catalyst due to thermal stress from the exhaust gas when the internal combustion engine is operated at a particularly high load. For example, there is a technique for increasing the amount of fuel contained in exhaust gas and utilizing the latent heat of vaporization, but increasing the amount of fuel in exhaust gas tends to increase the concentration of carbon monoxide, which is preferable from the viewpoint of emissions. Absent. As another technique for cooling the exhaust, there is a technique for attaching a water-cooled cooling adapter to the exhaust pipe. By using such a cooling adapter, it is possible to reduce catalyst stress due to exhaust heat during high-load operation. On the other hand, even if the exhaust temperature is relatively low such as during cold start of an internal combustion engine, the exhaust is cooled. Therefore, it becomes difficult to warm up the exhaust purification catalyst quickly. Thus, a technique is disclosed in which a heat insulating member is disposed in the vicinity of the exhaust port of the cylinder head to suppress heat transfer from the exhaust manifold to the cylinder head side where the cooling adapter is provided (for example, Patent Document 1). 2). For the same purpose, a technique for forming a non-contact portion in the flange portion so that the contact area between the cooling adapter and the exhaust manifold is reduced is disclosed (see, for example, Patent Document 3). .

  In addition, a coolant flow path is formed in the cylinder head of the internal combustion engine for cooling the internal combustion engine. Since the coolant flowing through the flow channel also takes heat of the exhaust gas through the exhaust passage, there may be a problem due to a decrease in the exhaust gas temperature. Thus, for example, in the technique shown in Patent Document 4, a structure of a mounting flange that prevents heat from being transmitted from the exhaust manifold side to the cylinder head has been proposed with regard to the structure of mounting the double pipe exhaust manifold to the cylinder head side.

JP 2004-156547 A JP 2002-115601 A JP 2011-169111 A JP-A-9-242537

  In the exhaust purification catalyst provided in the exhaust passage of the internal combustion engine, the catalyst temperature varies greatly depending on the temperature of the exhaust gas flowing into the exhaust purification catalyst. In an internal combustion engine having the above-described exhaust cooling configuration (for example, a cooling adapter, hereinafter referred to as “exhaust cooling configuration”), the exhaust cooled by the exhaust cooling configuration flows into the exhaust purification catalyst. It is possible to avoid an excessive temperature rise of the catalyst. On the other hand, when the exhaust gas temperature at the time when the operating state of the internal combustion engine belongs to the low load region and is discharged from the internal combustion engine is relatively low, the exhaust gas temperature is further lowered by the exhaust cooling configuration. It becomes difficult to maintain the temperature of the purification catalyst at a temperature suitable for exhaust purification, and there is a concern about deterioration of emissions.

Further, in the prior art, in considering the suppression of the exhaust temperature decrease, the cooling capacity itself by the exhaust cooling configuration provided on the cylinder head side of the internal combustion engine is considered, but it is not sufficient. In general, an internal combustion engine is provided with a plurality of cylinders, and an exhaust port is formed in the cylinder head corresponding to each cylinder. Here, the shape and arrangement of the exhaust ports are suitably adjusted according to various conditions such as the arrangement of cylinders in the internal combustion engine and the arrangement of exhaust branch pipes to be connected. The inventor of the present application has determined that the shape of the exhaust port or the like is an important factor for determining the exhaust temperature discharged from the exhaust port, that is, the temperature of the exhaust branch pipe into which the exhaust flows. It was found that the exhaust temperature exhausted from the exhaust port had a great influence on the heat transfer to the industrial structure. However, there is no fact in the prior art that the exhaust temperature has been reduced from this point of view. It is. Therefore, the conventional technology is not sufficient from the viewpoint of suitably maintaining the temperature of the exhaust purification catalyst provided in the exhaust passage.

  In addition, in order to suppress the heat transfer from the exhaust branch pipe to the exhaust cooling structure, the thermal distortion increases depending on the distribution and magnitude of the thermal stress generated in the vicinity of the exhaust branch pipe connected to the exhaust port. There is a possibility that an unfavorable situation may arise from the viewpoint of strength.

  The present invention has been made in view of the above-described problems, and is an exhaust cooling system for an internal combustion engine having an exhaust cooling configuration, in which the operating state of the internal combustion engine belongs to a low load region and is exhausted from the internal combustion engine. An object of the present invention is to provide an exhaust cooling system capable of realizing a preferable suppression of a decrease in exhaust temperature when the exhaust temperature at the time is relatively low.

  In the present invention, in order to solve the above-described problems, attention has been paid to the relationship between the shape and arrangement of the exhaust port formed in the cylinder head and the exhaust temperature discharged from the exhaust port as described above. This is because the state of heat transfer from the exhaust branch side to the exhaust cooling structure depends largely on the exhaust temperature discharged from the exhaust port to the exhaust branch side, and the state of thermal distortion generated in the vicinity of the exhaust branch pipe This is due to the fact that it greatly depends on the exhaust temperature.

  Specifically, the present invention has an exhaust branch pipe connected to each of a plurality of exhaust ports formed in the cylinder head corresponding to a plurality of cylinders, and is located downstream of the collection portion of each exhaust branch pipe. An exhaust cooling system for an internal combustion engine in which an exhaust purification catalyst is disposed in an exhaust pipe, the cooling section cooling the exhaust branch pipe or the exhaust port, and the exhaust branch pipe downstream from the cooling point by the cooling section A heat transfer inhibiting unit configured to inhibit heat transfer to the cooling unit, wherein the heat transfer inhibiting ability by the heat transfer inhibiting unit is obtained when the internal combustion engine is in a predetermined low load operation state. And a heat transfer inhibiting portion set such that the higher the exhaust temperature discharged from the exhaust port toward the exhaust branch pipe is, the greater the inhibition capability corresponding to the exhaust port is. The predetermined low-load operation state means a state in which the engine load is low to such an extent that the exhaust temperature decreases due to the cooling capacity of the cooling unit and it becomes difficult to maintain the activity of the exhaust purification catalyst. A load state in which idle operation is performed can be exemplified.

In the exhaust cooling system of the internal combustion engine, the exhaust flowing through the exhaust branch pipe is cooled by the cooling unit, and the cooled exhaust flows into the exhaust purification catalyst. Here, the cooling capacity of the cooling unit causes the cooling of the place where the cooling unit is installed and the heat transfer between the cooling unit and the exhaust branch pipe. In order to reduce the exhaust cooling effect during load operation, a heat transfer inhibition unit that inhibits heat transfer from the exhaust branch pipe to the cooling unit is disposed, and the internal combustion engine is in a predetermined low load operation state Depending on the exhaust temperature discharged from the exhaust port at that time, the inhibition capability by the heat transfer inhibition unit is set. In addition, as a mode of the inhibition, various modes can be used as long as the heat transfer from the exhaust branch pipe to the cooling unit is inhibited, that is, compared with the case where there is no heat transfer inhibiting unit. Can be adopted. For example, a heat insulating member may be employed as the heat transfer inhibiting portion, and the heat insulating member may be interposed between the cooling portion and the exhaust branch pipe. Further, the shape and material of the exhaust branch pipe may be adjusted so that heat transfer from the downstream side is difficult. By configuring the heat transfer inhibiting portion in this way, the movement of heat flowing from the exhaust branch pipe into the cooling portion is inhibited, and in particular, when the internal combustion engine is in a predetermined low load operation state, the heat transfer inhibiting portion The heat transfer inhibition from the exhaust branch pipe to the cooling part due to the above effectively suppresses the exhaust temperature drop.

  However, the shape and arrangement of the exhaust port formed in the cylinder head varies depending on the arrangement of the cylinder, the arrangement of the exhaust branch pipes, etc., and as a result, when the internal combustion engine is in a predetermined low load operation state, The exhaust temperatures discharged from the plurality of exhaust ports are not always the same. Therefore, the temperature of the exhaust branch pipe into which the exhaust flows also varies. As a result, the temperature difference between the exhaust branch pipe and the cooling section also differs depending on each exhaust port, and therefore, the factors that determine the heat transfer from the exhaust branch pipe to the cooling section are different for each exhaust port. become. The inventor of the present application pays attention to this point, and the inhibition capability of the heat transfer inhibition unit is such that the exhaust port whose exhaust temperature is higher from the exhaust port when the internal combustion engine is in a predetermined low load operation state, The heat transfer inhibition part was configured so that the inhibition ability corresponding to the port was increased. If the inhibition ability by the heat transfer unit inhibition part is set without considering the difference in exhaust temperature from each exhaust port, for example, if the inhibition ability is set uniformly, the inhibition ability by the heat transfer part inhibition part is excessive or insufficient Will occur. If the inhibition capacity becomes excessively large, the heat transfer to the cooling section can be inhibited, but the temperature difference between the exhaust branch pipe and the cooling section becomes large, and the thermal distortion in the vicinity of the exhaust branch pipe can be significant. Furthermore, when the internal combustion engine is operated at a high load, the heat load of the exhaust purification catalyst, which is the original purpose of the cooling unit, cannot be sufficiently reduced. Further, if the inhibition capacity is insufficient, the cooling capacity of the cooling unit is relatively increased, and it becomes difficult to sufficiently suppress the exhaust temperature decrease during low load operation.

  Therefore, by setting the inhibition capability by the heat transfer inhibition unit according to the exhaust temperature from the exhaust port when the internal combustion engine is in a predetermined low load operation state, by a suitable inhibition capability corresponding to each exhaust port, Heat transfer from the entire exhaust branch pipe to the cooling unit is preferably inhibited, and the influence of thermal distortion generated in the entire exhaust branch pipe can be suppressed as much as possible. More specifically, as described above, by setting the inhibition capability so that the exhaust port whose exhaust temperature from the exhaust port in a predetermined low-load operation state becomes higher, the inhibition capability corresponding to the exhaust port becomes larger, It is possible to achieve a balance between suppression of heat transfer from the entire branch pipe to the cooling section and suppression of thermal distortion in the entire exhaust branch pipe.

  Here, in the exhaust cooling system for an internal combustion engine, the plurality of exhaust ports have a curved portion having a relatively small curvature or a first exhaust port having a linear shape, and a curved portion having a relatively large curvature. It may be comprised so that at least the 2nd exhaust port which has these may be included. The exhaust temperature discharged from the first exhaust port in the predetermined low load operation state is higher than the exhaust temperature discharged from the second exhaust port in the predetermined low load operation state, and the heat transfer The inhibiting part is configured such that the inhibiting ability corresponding to the first exhaust port by the heat transfer inhibiting part is larger than the inhibiting ability corresponding to the second exhaust port by the heat transfer inhibiting part.

  The inventor of the present application paid attention to the exhaust cooling ability due to the shape of the exhaust port. When the exhaust port has a bent portion that changes the direction of the flow of exhaust gas, attention was paid to the fact that the higher the curvature of the bent portion, the higher the temperature of the exhaust port. And since the temperature of the exhaust port becomes higher in this way, it means that more heat is taken from the exhaust, and thus the ability to cool the exhaust exhaust from the exhaust port is great. As described above, when the first exhaust port and the second exhaust port are at least provided, the second exhaust port has a bent portion having a relatively larger curvature than the first exhaust port. The exhaust gas discharged from the exhaust gas is cooled more, and the exhaust gas temperature discharged from the first exhaust port becomes higher. As a result, the temperature of the exhaust branch pipe connected to the first exhaust port is higher than that of the exhaust branch pipe connected to the second exhaust port. Therefore, by setting the inhibition capacity corresponding to the first exhaust branch pipe port larger than the inhibition capacity corresponding to the second exhaust port, it is possible to suppress heat transfer from the entire exhaust branch pipe to the cooling section and A balance of thermal strain suppression can be achieved.

  Further, in the exhaust cooling system of the internal combustion engine, the second exhaust port has a connection portion bending portion different from the bending portion having a relatively large curvature at the connection portion with the exhaust branch pipe. The connection part bend part may have an inner bend part with a relatively small bend radius and an outer bend part with a relatively large bend radius. In this case, the temperature of the inner bent portion in the predetermined low-load operation state is higher than the temperature of the outer bent portion in the predetermined low-load operation state, and the second exhaust port by the heat transfer inhibition portion The corresponding inhibition ability is set corresponding to each of the inner bending portion and the outer bending portion, and the inhibition ability corresponding to the outer bending portion is set larger than the inhibition ability corresponding to the inner bending portion. The

  As described above, the exhaust temperature discharged from the second exhaust port due to its cooling capacity is lower than the exhaust from the first exhaust port. However, when focusing only on the second exhaust port, if the second exhaust port has an inner bent portion and an outer bent portion in the vicinity of the connection portion with the exhaust branch pipe, the cooling caused by the exhaust port shape described above. Like the capacity, the inner bend is more likely to be hotter than the outer bend, so the exhaust temperature that flows into the exhaust branch through the vicinity of the inner bend is deprived of more heat by the inner bend. It becomes lower than the exhaust temperature which flows into the exhaust branch pipe through the vicinity of the bent portion. Therefore, based on this point, by setting the inhibition capacity corresponding to the outer bent portion with respect to the second exhaust port larger than the inhibition capacity corresponding to the inner bent portion, the heat transfer from the entire exhaust branch pipe to the cooling portion is suppressed. And the balance of suppression of thermal distortion in the entire exhaust branch pipe can be achieved more effectively. In this case, it is preferable that the inhibition capability corresponding to the outer bent portion is set lower than the inhibition capability corresponding to the first exhaust port.

  In the exhaust cooling system for an internal combustion engine, the plurality of cylinders may be a first cylinder and a second cylinder configured to have different intake air amounts supplied from an intake passage, and the predetermined low-load operation may be performed. In the state, it may be configured to include at least a first cylinder in which the air-fuel ratio in the cylinder is relatively lean and a second cylinder in which the air-fuel ratio in the cylinder is relatively rich. . The exhaust temperature discharged from the first exhaust port corresponding to the first cylinder in the predetermined low load operation state is from the second exhaust port corresponding to the second cylinder in the predetermined low load operation state. It is higher than the exhaust temperature to be discharged, and the heat transfer inhibition unit has an inhibition capability corresponding to the first exhaust port by the heat transfer inhibition unit, and the inhibition capability corresponding to the second exhaust port by the heat transfer inhibition unit. Configured to be greater than ability.

  The inventor of the present application focused on the variation in the intake air amount supplied from the intake passage to the cylinder with respect to the variation in the exhaust temperature discharged from the exhaust port. Depending on the configuration and arrangement of the internal combustion engine, when intake air is supplied to a plurality of cylinders from the intake passage, there may be a cylinder in which the intake air easily flows and a cylinder in which the intake air is less likely to flow. For this reason, the air-fuel ratio of the air-fuel mixture formed in the cylinder may vary due to the structural reasons of the internal combustion engine. When the air-fuel ratio becomes relatively rich, it is greatly affected by the latent heat of vaporization of the contained fuel, so that the exhaust temperature after combustion tends to be lower than that when the air-fuel ratio is relatively lean. . When the exhaust temperature discharged from the exhaust port may vary due to the structural reasons of the internal combustion engine as described above, by increasing the inhibition capability corresponding to the exhaust port where the exhaust temperature becomes high as described above. Thus, it is possible to achieve a balance between suppression of heat transfer from the entire exhaust branch pipe to the cooling unit and suppression of thermal distortion in the entire exhaust branch pipe.

Here, in the cooling system for an internal combustion engine, the cooling unit is a cooling adapter that cools a part of the exhaust branch pipe, and the cooling adapter includes the exhaust gas located upstream of the collecting unit. The other part of the branch pipe is connected, and the heat transfer inhibiting part is an end face of the cooling adapter on the side to which the other part of the exhaust branch pipe is connected, and the exhaust branch pipe on the side connected to the cooling adapter. The flange of the other part, the gasket disposed between the end face of the cooling adapter and the flange, and the other part of the exhaust branch pipe are formed in at least one of predetermined portions from the flange to the gathering part. Also good.

  When the exhaust branch pipe is cooled by the cooling adapter in this way, the cooling unit is disposed outside the cylinder head. Therefore, in order to effectively inhibit the transfer of heat from the exhaust to the exhaust branch pipe and escape from there to the cooling section, it is preferable that the heat transfer inhibiting section is formed at the above location. In addition, when a heat transfer inhibition part is formed in the flange and gasket, the entire flange and gasket may be configured to inhibit heat transfer. Further, the predetermined portion where the heat transfer inhibiting portion is formed may be a portion where the temperature is easily increased locally in the exhaust branch pipe.

  Alternatively, in the internal combustion engine cooling system, the cooling unit is a cooling device that cools the exhaust port, and the heat transfer inhibiting unit is the cylinder head to which the exhaust branch pipe is connected. A connecting portion of the exhaust branch pipe on the side connected to the cylinder head, a gasket disposed between the connecting portion and the flange, and from the flange to the collecting portion in the exhaust branch pipe You may form in at least any one of predetermined parts. Thereby, the inhibition of the effective heat transfer from the exhaust branch pipe to the cooling unit is realized.

  According to the present invention, in an exhaust cooling system for an internal combustion engine having a configuration for exhaust cooling, it is preferable when the operating state of the internal combustion engine belongs to a low load region and the exhaust temperature at the time of exhaust from the internal combustion engine is relatively low. Therefore, it is possible to realize a reduction in the exhaust temperature.

1 is a first diagram showing a schematic configuration of an exhaust cooling system for an internal combustion engine according to the present invention. It is a figure which shows the structure of the exhaust port formed in the cylinder head of the internal combustion engine shown in FIG. FIG. 2 is a view showing a configuration of a heat insulating gasket disposed between a cooling adapter and a flange of a downstream side exhaust branch pipe in the exhaust cooling system of the internal combustion engine shown in FIG. 1. It is the figure which showed schematically the heat transfer in the exhaust system of an internal combustion engine. It is a figure which shows the correlation with the heat insulation of the heat insulation gasket provided between the exhaust branch pipe and the cylinder block, and the wall surface temperature of an exhaust branch pipe. It is a figure which shows the flow of the exhaust_gas | exhaustion in an exhaust port when the bending angle of an exhaust port is 30 degree | times, 60 degree | times, and 90 degree | times. It is a figure which shows the temperature distribution of a head wall when the bend angle of an exhaust port is 30 degree | times and 90 degree | times. It is a figure which shows the exhaust cooling allowance by the exhaust port of four cylinders contained in an internal combustion engine. It is a figure which shows the correlation with the heat insulation of the heat insulation gasket in cylinder # 1 and # 2 at the time of low load driving | running | working of an internal combustion engine, the gas temperature to enter into an exhaust branch pipe, and the wall surface temperature of an exhaust branch pipe. It is a figure which shows the correlation with the heat insulation of a heat insulation gasket at the time of high load driving | operation of an internal combustion engine, the wall surface temperature of an exhaust branch pipe, and the cooling adapter temperature. FIG. 3 is a view showing another structure around the exhaust branch pipe of the internal combustion engine shown in FIG. 1. FIG. 6 is a view showing another configuration of a heat insulating gasket disposed between the cooling adapter and the flange of the downstream exhaust branch pipe in the exhaust cooling system for the internal combustion engine shown in FIG. 1.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  Embodiments of an exhaust cooling system for an internal combustion engine according to the present invention will be described with reference to the drawings attached to this specification. FIG. 1 is a diagram illustrating a schematic configuration of an exhaust cooling system for an internal combustion engine according to the present embodiment, and a schematic configuration of an internal combustion engine 1 including the system. The internal combustion engine 1 is a spark ignition type internal combustion engine (gasoline engine) having four cylinders 2. However, when the four cylinders 2 are displayed separately as shown in FIG. The number (# 1 to # 4) for discrimination is described after the reference number 2 of the cylinder. In FIG. 1, only one of the four cylinders (for example, cylinder 2 # 2) is illustrated, and a cooling adapter provided corresponding to a cylinder (for example, cylinder 2 # 1) not illustrated. 10 and an exhaust branch pipe 9 are also shown. 2 shows a configuration of an exhaust port formed in the cylinder head 1a of the internal combustion engine 1. FIG. 3 shows a cooling adapter 10 and an exhaust branch pipe connected to the cooling adapter 10 (a downstream exhaust described later). The structure of the heat insulation gasket 11 arrange | positioned between branch pipes 9b) is shown.

  A spark plug 3 is attached to each cylinder 2 of the internal combustion engine 1, and an intake port 4 and an exhaust port 5 are provided in the cylinder head 1a. The intake port 4 is a passage that guides air and fuel into the cylinder 2 of the internal combustion engine 1, and is opened and closed by an intake valve 6. The intake port 4 is connected to an intake passage (not shown), and fresh air (air) is taken from the atmosphere. A fuel injection valve 8 is attached so that fuel can be injected into the intake port 4. The exhaust port 5 is a passage for exhausting the gas burned in the cylinder 2 (burned gas) from the cylinder 2 and is opened and closed by the exhaust valve 7. As shown in FIG. 2, when the exhaust ports 5 are distinguished from each other in correspondence with the respective cylinders as shown in FIG. 2, the exhaust port reference number 5 is followed by a distinguishing number (# 1 To # 4). An exhaust branch pipe 9 is connected to each exhaust port 5 corresponding to each cylinder 2. The exhaust branch pipe 9 is formed of an upstream exhaust branch pipe 9a and a downstream exhaust branch pipe 9b as will be described later. When the upstream side exhaust branch pipe 9a or the downstream side exhaust branch pipe 9b is distinguished and displayed corresponding to each cylinder, the reference number 9a or 9b of each exhaust branch pipe is followed by a number ( # 1 to # 4) are described. Then, the four downstream exhaust branch pipes 9b # 1 to 9b # 4 corresponding to the four cylinders merge at the gathering portion 9e as shown in FIG. 1, and are connected to the exhaust pipe 12 downstream thereof. The exhaust pipe 12 is provided with an exhaust purification catalyst 20 for performing exhaust purification. As the exhaust purification catalyst 20, for example, an oxidation catalyst, a three-way catalyst, an occlusion reduction type NOx catalyst, a selective reduction type NOx catalyst, or the like is used. Can be mentioned.

  Here, as shown in FIG. 1, in the internal combustion engine 1, a cooling adapter 10 for cooling the exhaust flowing through the exhaust branch pipe 9 is provided in each exhaust branch pipe. Specifically, the cooling adapter 10 has a cooling water passage 10 a through which cooling water circulates, and the cooling surface of the cooling adapter 10 is one of the exhaust branch pipes 9 immediately downstream of the exhaust port 5. It arrange | positions so that the outer periphery of the upstream exhaust branch pipe 9a which is a part may be covered. The cooling water channel 10a of the cooling adapter 10 may be configured to be connected to a cooling water channel of the internal combustion engine 1 (not shown) so that the cooling water is circulated by a common circulation pump. The cooling water may be circulated independently. This upstream side exhaust branch pipe 9 a becomes a portion that is directly cooled by the cooling adapter 10.

Further, downstream of the upstream exhaust branch pipe 9a, a downstream exhaust branch pipe 9b that forms an exhaust passage as an exhaust branch pipe to the collecting portion 9e is provided. The downstream exhaust branch pipe 9b is provided with a connection flange 9c on the upstream exhaust branch pipe 9a side, and the downstream side with the heat insulating gasket 11 sandwiched between the connection flange 9c and the upstream exhaust branch pipe 9a. The side exhaust branch pipe 9b and the upstream side exhaust branch pipe 9a are connected. In addition, the connection flange 9c is integrally formed with respect to the four downstream exhaust branch pipes 9b # 1 to 9b # 4, and is provided on the through hole provided on the flange and the upstream exhaust branch pipe 9a side. Using the screw hole 13, the connection flange 9c and the upstream side exhaust branch pipe 9a are connected. Specifically, a stud bolt attached to the screw hole 13 is passed through the through hole and fixed with a nut so that the two are connected. In addition, although the said heat insulation gasket 11 is corresponded to the heat transfer inhibition part which concerns on this invention, the detail is mentioned later.

  Thus, in the internal combustion engine 1 provided with the cooling adapter 10 that cools the exhaust flowing through the upstream side exhaust branch pipe 9a, by reducing the exhaust temperature discharged from the internal combustion engine 1, the components installed in the exhaust system can be reduced. The applied thermal load can be reduced, and the life of parts can be extended. In particular, it is possible to reduce the amount of noble metal contained in the exhaust purification catalyst by suppressing the increase in the exhaust temperature flowing into the exhaust purification catalyst 20. As an alternative technique, the amount of fuel contained in the exhaust gas can be increased and the exhaust temperature can be lowered by the latent heat of vaporization. However, the deterioration of fuel consumption and the emission caused by the increase of fuel (for example, monoxide) (Increased carbon concentration) is likely to occur. Therefore, the exhaust cooling by the cooling adapter 10 is useful from the viewpoint of improving the exhaust gas purification characteristics of the internal combustion engine 1.

  On the other hand, when the exhaust gas temperature discharged from the internal combustion engine 1 is relatively low, that is, when the internal combustion engine 1 is performing a low load operation (for example, when the exhaust enthalpy is lower than 10 to 20 kW or when performing idle operation) If the exhaust cooling is performed by the cooling adapter 10, the exhaust temperature flowing into the exhaust purification catalyst 20 becomes excessively low, and as a result, the exhaust purification efficiency by the exhaust purification catalyst 20 may be significantly reduced. . Therefore, in the present invention, heat transfer from the downstream exhaust branch pipe 9b connected to the upstream exhaust branch pipe 9a directly cooled by the cooling adapter 10 to which the exhaust flowing into the exhaust purification catalyst 20 flows is transferred to the cooling adapter 10. In consideration of the above, an exhaust cooling system for suppressing a decrease in exhaust temperature when the internal combustion engine 1 is operated at a low load was constructed.

  Here, the upper part (a) of FIG. 4 schematically shows the heat transfer performed between the cylinder head 1a having the exhaust port 5 and the passage wall of the exhaust branch pipe 9 when the cooling adapter 10 is not provided. It is the figure shown in. In this case, the heat generated by the combustion in the cylinder 2 moves to the cylinder head 1a as heat radiation Q1, and the heat of the cylinder head 1a moves to the atmosphere (ambient atmosphere) as heat radiation Q3. Further, in the exhaust branch pipe 9, the heat of the exhaust flowing through the exhaust branch pipe 9 is transferred as heat radiation Q2 from the exhaust to the exhaust branch pipe 9, and the heat of the exhaust branch pipe 9 is transferred as heat dissipation Q4. Move to the atmosphere. When the internal combustion engine 1 is operating at a low load, the engine temperature of the internal combustion engine 1 is not sufficiently increased. On the other hand, the exhaust branch 9 is exposed to the exhaust gas after combustion. It tends to be higher than the temperature of the cylinder head 1a. Therefore, heat moves as heat transfer Q5 from the exhaust branch pipe 9 to the cylinder head 1a.

  Next, heat transfer in the case where the cooling adapter 10 is provided will be described based on the lower part (b) of FIG. In FIG. 3, which is a schematic illustration, the upstream exhaust branch pipe 9 a that is directly cooled by the cooling adapter 10 can be regarded as being integral with the cooling adapter 10. Therefore, in FIG. 4B illustrating the heat transfer, the exhaust branch pipe wall on the downstream side exhaust branch pipe 9b side is arranged next to the exhaust branch pipe wall on the cooling adapter 10 side. Here, the heat transfer in the cylinder head 1a is as described based on FIG. 4A, and the heat dissipation Q11 in FIG. 4B corresponds to the heat dissipation Q1 in FIG. The heat dissipation Q13 in FIG. 4 (b) corresponds to the heat dissipation Q3 in FIG. 4 (a). In the cooling adapter 10 as well, heat moves as heat radiation Q16 from the exhaust flowing through the upstream side exhaust branch pipe 9a. This heat transfer is direct exhaust cooling by the cooling adapter 10.

Similarly, in the downstream exhaust branch pipe 9b, the heat of the exhaust flowing through the downstream exhaust branch pipe 9b moves from the exhaust to the downstream exhaust branch pipe 9b as heat radiation Q12, and on the downstream side. The heat of the exhaust branch pipe 9b moves to the atmosphere as heat radiation Q14. Here, if the cooling adapter 10 exists, heat transfer Q15 from the downstream exhaust branch pipe 9b to the cooling adapter 10 is generated by the cooling capacity. Here, since the cooling adapter 10 is a water-cooling type, its cooling capacity is relatively large. Therefore, the temperature gradient in the exhaust passage wall extending from the cooling adapter 10 to the downstream exhaust branch pipe 9b becomes large. As a result, the heat quantity of the heat transfer Q15 is larger than the heat quantity of the heat transfer Q5 shown in FIG. Become very large. As a result, heat dissipation in the downstream exhaust branch pipe 9b is promoted, and the amount of heat of the heat dissipation Q12 and Q14 tends to be larger than the amount of heat of the heat dissipation Q2 and Q4 shown in FIG. is there. Thus, it can be understood that the presence of the cooling adapter 10 allows the heat transfer generated in the exhaust branch pipe 9 to promote the decrease in the exhaust temperature with the heat transfer Q15 as a base point. This lowering effect of the exhaust temperature is particularly prominent when the internal combustion engine 1 is operating at a low load from the viewpoint of the purification ability of the exhaust purification catalyst 20.

  By providing the cooling adapter 10 in this way, the life of the exhaust system parts can be extended and the exhaust gas purification characteristics of the internal combustion engine 1 can be improved. On the other hand, there is a concern that the exhaust gas temperature may be lowered during low load operation of the internal combustion engine 1. . Therefore, in the present invention, paying attention to the heat transfer Q15 which is the base point of heat transfer caused by the cooling adapter 10 shown in FIG. Specifically, as shown in FIG. 1, in order to inhibit the heat transfer Q15, it has a function as a gasket between the connection flange 9c of the downstream exhaust branch pipe 9b and the cooling adapter 10, and the upstream side A heat insulating gasket 11 is provided that has a heat insulating ability, that is, a material having a low heat penetration rate, that is, SUS that is a material of the exhaust branch pipe 9a and the downstream exhaust branch pipe 9b.

Here, the influence of the heat insulating gasket 11 on the passage wall surface temperature of the downstream side exhaust branch pipe 9b will be described in detail with reference to FIG. FIG. 5 shows the heat transmissivity of the heat insulating gasket 11 and the downstream exhaust when the heat insulating gasket 11 is disposed between the upstream exhaust branch pipe 9a and the downstream exhaust branch pipe 9b in the internal combustion engine 1 shown in FIG. The correlation with the passage wall surface temperature of the branch pipe 9b is represented. The correlation indicated by the line L1 in the figure is a correlation when the downstream exhaust branch pipe 9b is covered with the shroud, and the correlation indicated by the line L2 is a correlation when the downstream exhaust branch pipe 9b is covered with the shroud. It is the correlation when not. Here, the heat transmissivity is calculated by the following equation from the heat resistance value (R1,..., Rn) for each material obtained by dividing the thermal conductivity of one or more materials constituting the heat insulating gasket 11 by the thickness. It is calculated according to 1. It means that heat insulation is so high that the value of a heat transmissivity is small.
Thermal conductivity = 1 / Σ (R1 + ... + Rn) (Formula 1)

  When the heat insulating property of the heat insulating gasket 11 increases, the wall surface temperature of the downstream side exhaust branch pipe 9b increases as indicated by the lines L1 and L2. This is because the heat transfer (heat transfer Q15) transmitted from the passage wall of the downstream exhaust branch pipe 9b to the wall of the upstream exhaust branch pipe 9a is hindered by the heat insulating gasket 11, and thus the wall of the downstream exhaust branch pipe 9b. It means that a lot of heat stays. Here, when a large amount of heat is accumulated in the downstream side exhaust branch pipe 9b, in particular, the connection flange 9c located at the end thereof is likely to have a high temperature, and there is a concern about an increase in thermal stress and generation of thermal distortion. Furthermore, exhaust flows into the four exhaust branch pipes 9 provided in the internal combustion engine 1 via the corresponding exhaust ports 5. The exhaust cooling capacity of the exhaust ports 5 depends on each port. Therefore, the exhaust temperature discharged from the exhaust port 5 is not necessarily the same because the heat is taken away by each exhaust port 5. Therefore, in the state where the internal combustion engine 1 is operating at a low load, the wall surface temperature of each exhaust branch pipe 9 into which exhaust from the exhaust port 5 flows varies depending on the cooling capacity of the exhaust port 5, and temporarily If the heat insulating property of the heat insulating gasket 11 disposed between the connection flange 9c and the cooling unit 10 is set to have a predetermined heat transmissibility uniformly, the heat insulating property will be excessive or insufficient.

For example, if the heat insulating property of the heat insulating gasket 11 is uniformly excessively increased, the heat transfer Q15 to the cooling adapter 10 can be sufficiently inhibited, but the connection flange 9c is heated to a problem such as thermal stress. Becomes apparent. Further, when the internal combustion engine is in a high-load operation state, the exhaust cooling capacity that is originally required cannot be ensured, and it becomes difficult to reduce the heat load of the exhaust purification catalyst 20. On the other hand, if the heat insulating property of the heat insulating gasket 11 is uniformly lowered, it is difficult to sufficiently suppress the reduction in the exhaust temperature. Therefore, in the exhaust cooling system of the internal combustion engine 1 according to the present invention, each exhaust port is considered in consideration of the exhaust cooling capacity of the exhaust ports 5 # 1 to 5 # 4 when the internal combustion engine 1 is in a low load operation state. The heat insulating properties of the heat insulating gaskets 11 arranged between the respective downstream side exhaust branch pipes 9b # 1 to 9b # 4 and the cooling adapter 10 are set so as to be partially different depending on the exhaust temperature discharged from the air.

  Here, when examining the exhaust cooling capacity of the exhaust port 5, the inventor of the present application has a case where the exhaust port 5 is bent between a portion where the exhaust valve 7 is disposed and a portion where the exhaust branch pipe 9 is connected. The inventor of the present application paid attention to the fact that the temperature of the passage wall in the head (hereinafter also referred to as “head wall”) tends to increase due to the heat of the exhaust as the curvature of the bent portion increases. When the temperature of the head wall forming the exhaust port 5 becomes higher due to the exhaust heat, the exhaust heat is taken away there, which means that the cooling capacity for the exhaust is high. Therefore, the temperature of the bent portion 5d of the exhaust port 5 and the curvature of the bent portion 5d will be described below with reference to FIGS. In addition, the shift | offset | difference of the extension direction of the exhaust port in the entrance and exit of a bending part is defined as the bending angle of a bending part. In FIG. 6, it is comprised so that the curvature may become large, so that the bending angle of a bending part becomes large.

  FIG. 6 shows a part of the exhaust port 5 having bent portions 5d having bend angles of 30 degrees, 60 degrees, and 90 degrees, respectively, and having the same cross-sectional area with respect to the flow of exhaust gas. The state of the exhaust gas flow rate when exhaust gas having a predetermined enthalpy during load operation is flowing is shown. Specifically, in the bending portion 5d, the left side in the drawing is an inner bending portion having a small bending radius, and the right side in the drawing is an outer bending portion having a large bending radius. In the bent portion 5d, the exhaust flow velocity is displayed in shades, and is displayed darker as the exhaust flow velocity is higher.

  As can be understood from FIG. 6, a region where the exhaust flow velocity is relatively high is formed in a region adjacent to the inner bend, and the region becomes larger as the bend angle increases. As a result, a region R1 where the exhaust flow velocity is relatively low and a region R2 where the exhaust flow velocity is relatively high are formed on the downstream side of the bent portion 5d. The region R1 where the exhaust flow velocity becomes relatively low increases as the bend angle of the bent portion 5d increases, and when the bend angle reaches 90 degrees, separation of the exhaust flow occurs, which is indicated by the oblique lines in FIG. In the region R1, the backflow is born.

  As the bending angle of the bent portion 5d increases, the vertical component of the exhaust that hits the inner wall surface of the inner bent portion increases, and a high-speed exhaust flow is formed near the inner wall surface of the inner bent portion as shown in FIG. . For this reason, the inner bent portion is particularly likely to be heated. In addition, as described above, when the bend angle becomes large and the exhaust flow is separated, the exhaust flow is disturbed at the outlet of the inner bend, which is a factor that causes the upstream inner bend to have a high temperature. Conceivable. Therefore, FIG. 7 shows the heat distribution in the head wall of the bending portion 5d having a bending angle of 30 degrees and the heat distribution in the head wall of the bending portion 5d having a bending angle of 90 degrees. It should be noted that the heat distribution in both figures is darker as the temperature is higher. As can be understood from FIG. 7, when the bending angle of the bending portion 5d is small, the temperature difference between the head wall surface is not so large between the inner bending portion and the outer bending portion, but when the bending angle of the bending portion 5d increases, The temperature of the head wall surface at the bent portion tends to be higher than the temperature of the head wall surface at the outer bent portion.

As described above, when the curvature or the bending angle of the bent portion 5d of the exhaust port 5 is increased, the temperature of the head wall surface at the inner bent portion is significantly increased. This means that the bent portion 5d of the exhaust port 5
This means that the exhaust cooling capacity of the exhaust port 5 varies depending on the shape of the exhaust port 5. In the internal combustion engine 1 in the present embodiment, as shown in FIG. 2, four cylinders 2 # 1 to 2 # 4 are arranged in series, and the outlets of the exhaust ports 5 # 1 to 5 # 4 corresponding to each cylinder ( Each exhaust port 5 is formed such that the opening on the side connected to the exhaust branch pipe 9 is gathered at a substantially central portion of the arrangement of the cylinders 2. Therefore, the exhaust ports 5 # 1, 5 # 4 corresponding to the cylinders 2 # 1, 2 # 4 located outside the row are the exhaust ports 5 corresponding to the cylinders 2 # 2, 2 # 3 located inside the row. Compared to # 2, 5 # 3, the curvature of the bent portion is increased.

  As a result, the exhaust cooling capacity by the exhaust ports 5 # 1, 5 # 4 becomes larger than the exhaust cooling capacity by the exhaust ports 5 # 2, 5 # 3. In an internal combustion engine having an exhaust port substantially the same as the shape shown in FIG. 2, the cooling capacity (exhaust cooling allowance) of the exhaust port corresponding to each cylinder when the low load operation is performed is two shapes. The graph compared for every exhaust port in the pattern is shown in FIG. The exhaust cooling allowance is defined as a difference between an inlet gas temperature to the exhaust port 5 and an outlet gas temperature from the exhaust port. Although the value of the exhaust cooling allowance varies depending on the shape and size of the actual exhaust port, the exhaust cooling capacity by the exhaust ports 5 # 1 and 5 # 4 having the relatively large curved portions is relatively curved. It can be understood that the exhaust gas tends to be larger than the exhaust cooling capacity by the exhaust ports 5 # 2, 5 # 3 having a small bent portion.

  The exhaust cooling capacity of the exhaust port 5 is increased, so that the exhaust temperature flowing into the exhaust branch pipe 9 connected to the exhaust port 5 is reduced, and the temperature difference between the cooling adapter 10 and the downstream exhaust branch pipe 9b is small. Become. On the other hand, since the exhaust cooling capacity of the exhaust port 5 is reduced, the exhaust gas having a relatively high temperature flows into the exhaust branch pipe 9 connected to the exhaust port 5. The temperature difference between the adapter 10 and the downstream exhaust branch pipe 9b becomes large. Therefore, the heat insulating property of the heat insulating gasket 11 is set in consideration of the variation in the heat transfer condition from the downstream side exhaust branch pipe 9b to the cooling adapter 10 due to such a difference in the exhaust cooling ability of the exhaust port 5.

  Here, in the upper part (a) of FIG. 9, when the internal combustion engine 1 is operating at a low load, the correlation between the heat flow rate of the heat insulating gasket 11 and the temperature of the gas entering the downstream exhaust branch pipe 9b # 1. (Correlation indicated by line L3) and the correlation (correlation indicated by line L4) between the heat permeability of the heat insulating gasket 11 and the wall surface temperature of the downstream exhaust branch pipe 9b # 1. Furthermore, the lower part (b) of FIG. 9 shows the correlation between the heat flow rate of the heat insulating gasket 11 and the temperature of the gas entering the downstream exhaust branch pipe 9b # 2 when the internal combustion engine 1 is operating at a low load. (Correlation indicated by line L5) and the correlation (correlation indicated by line L6) between the heat flow rate of the heat insulating gasket 11 and the wall surface temperature of the downstream exhaust branch pipe 9b # 2. FIG. 10 shows the correlation (correlation indicated by the line L7) between the heat flow rate of the heat insulating gasket 11 and the wall surface temperature of the downstream side exhaust branch pipe 9b when the internal combustion engine 1 is operating at a high load. The correlation (correlation shown by the line L8) of the heat flow rate of the heat insulation gasket 11 and the wall surface temperature of the upstream exhaust branch pipe 9a # 1 cooled by the cooling adapter 10 is shown. In addition, although the inlet gas temperature to the downstream side exhaust branch pipes 9b # 1 and 9b # 2 passes through the cooling adapter 10, the exhaust temperature discharged from the corresponding exhaust ports 5 # 1 and 5 # 2 is It is thought to reflect.

As shown in FIG. 9, even if the heat insulating property of the heat insulating gasket 11 is changed as appropriate, the temperature of the gas entering the downstream exhaust branch 9b # 2 is about 10 times the temperature of the gas entering the downstream exhaust branch 9b # 1. The reason for the high degree is considered to be that the exhaust cooling capability by the exhaust port 5 # 2 is lower than the exhaust cooling capability by the exhaust port 5 # 1 as described above. Further, even when the wall surface temperatures of the downstream exhaust branch pipe 9b # 1 and the downstream exhaust branch pipe 9b # 2 are compared, the wall surface temperature of the downstream exhaust branch pipe 9b # 2 is similarly the downstream exhaust branch pipe. It is higher than the wall surface temperature of 9b # 1. Here, considering that the heat transfer Q15 increases as the difference between the wall temperature of the cooling adapter 10 and the downstream exhaust branch pipe 9b increases, the exhaust port 5 # in which the exhaust temperature discharged during low load operation increases. 2. In other words, the heat insulating property of a predetermined portion of the heat insulating gasket 11 corresponding to the exhaust port 5 # 2 having a relatively small exhaust cooling capacity is the heat insulating property corresponding to the exhaust port 5 # 1 having a relatively large exhaust cooling capacity. It sets so that it may become higher than the heat insulation of the predetermined part of the gasket 11. FIG. As a result, the heat insulation performance of the heat insulating gasket 11 is relatively low for the exhaust port 5 # 1 where the exhaust temperature discharged at the time of low load operation is relatively low, but the temperature at which the heat transfer Q15 is increased there. Since the difference is small, the influence on the suppression of the decrease in the exhaust temperature can be reduced even if such heat insulation is set.

  When the internal combustion engine 1 is operating at a high load, the wall surface temperature of the upstream exhaust branch pipe 9a on the cooling adapter 10 side is substantially constant regardless of the heat insulating property of the heat insulating gasket 11, as shown in FIG. However, the wall surface temperature of the downstream side exhaust branch pipe 9b increases as the heat insulating property of the heat insulating gasket 11 increases. Here, as described above, since the heat insulating property of the predetermined portion of the heat insulating gasket 11 corresponding to the exhaust port 5 # 1 is set to be relatively low, the heat accumulated on the connection flange 9c side is cooled. Therefore, it is possible to reduce the wall surface temperature of the downstream side exhaust branch pipe 9b # 1 during high load operation, and to simultaneously reduce problems such as thermal stress at the connection flange 9c.

  Specifically, as shown in FIG. 3, the exhaust cooling capacity of the exhaust ports 5 # 1, 5 # 4 is larger than the exhaust cooling capacity of the exhaust ports 5 # 2, 5 # 3, and as a result, the exhaust port 5 exhausts from the exhaust port. The exhaust temperature is relatively low. Therefore, in the heat insulating gasket 11, the heat insulating property of the portion 11b corresponding to the exhaust ports 5 # 1, 5 # 4 is relatively increased, and the heat insulating property of the portion 11a corresponding to the exhaust ports 5 # 2, 5 # 3 is increased. Set relatively high. For example, the part 11a is formed of a damper having a relatively high heat insulating property, and the part 11b is formed of a ceramic having a relatively low heat insulating property. By setting such heat insulation, it balances the suppression of heat transfer (heat transfer Q15) from the entire exhaust branch pipe to the cooling adapter 10 and the suppression of thermal stress etc. in the exhaust branch pipe, particularly the connection flange 9c. I can plan well.

  The heat insulating gasket 11 may be formed so as to integrally include the portions 11a and 11b, or may be formed separately for each portion. Further, instead of changing the material of the heat insulating gasket 11, the heat insulating properties of the portions 11a and 11b may be adjusted to be a desired heat insulating property by changing the thickness or sandwiching another member.

  Further, as shown in FIG. 3, the interval between the upstream exhaust branch pipes 9a # 2 and 9a # 3 corresponding to the exhaust ports 5 # 2 and 5 # 3 having a relatively high exhaust gas temperature is set as the exhaust port 5. It is wider than the interval between the upstream exhaust branch pipes 9a # 1 and 9a # 4 corresponding to # 1, 5 # 4. This is because the downstream exhaust branch pipes 9b # 2 and 9b # to be connected are affected by the influence of radiant heat from the upstream exhaust branch pipes 9a # 2 and 9a # 3 due to the relatively high exhaust gas temperature. This is to prevent the temperature of 3 from increasing as much as possible.

<Modification 1>
In the above-described embodiments, the heat insulating gasket 11 is used as the heat transfer inhibiting portion, but the following forms can also be adopted as another method. First, the end face 10b of the cooling adapter 10 to which the connection flange 9c of the downstream side exhaust branch pipe 9b is connected may be formed so as to obtain heat insulation corresponding to the portions 11a and 11b of the heat insulation gasket 11. Specifically, the end face 10b is formed of a predetermined heat insulating member having heat insulating properties to be set, or the contact area with the connection flange 9c is adjusted, so that heat from the downstream exhaust branch pipe 9b can be adjusted. Adjust heat transmissivity for inflow. Similarly, the connection flange 9c connected to the cooling adapter 10 may be formed so as to obtain heat insulation corresponding to the portions 11a and 11b of the heat insulation gasket 11.

Further, in the downstream side exhaust branch pipe 9b, heat insulation Q15 from the downstream side exhaust branch pipe 9b to the cooling adapter 10 is improved by enhancing the heat insulation of a predetermined portion of the branch pipe wall between the connection flange 9c and the collecting portion 9e. May be inhibited. Specifically, as shown in FIG. 11, the thickness T1 of the exhaust branch pipe wall of the predetermined part 9f of the exhaust branch pipe near the connection flange 9c is made thinner than the thickness T2 of the exhaust branch pipe wall of the other part. Thus, the inhibition ability of the heat transfer Q15 may be adjusted. For example, the smaller the T1, the greater the ability to inhibit the heat transfer Q15, and the longer the length L10 of the predetermined portion 9f, the greater the ability to inhibit the heat transfer Q15. Therefore, the ability to inhibit the heat transfer Q15 according to the temperature of the downstream side exhaust branch pipe 9b during low load operation can be set according to the technical idea of the present invention, using the sizes of T1 and L10 as parameters.

  The specific form of the heat transfer inhibiting portion shown in this way is not necessarily limited to one, and a plurality of forms can be adopted at the same time.

<Modification 2>
In the above-described embodiment, the cooling unit (cooling adapter) 10 is mounted outside the cylinder head 1a. However, instead of this mode, a mode in which the cooling unit is incorporated in the cylinder head 1a may be employed. . In this case, the exhaust flowing through the exhaust port 5 is cooled by the built-in cooling unit. Even in such an embodiment, the exhaust temperature flowing into the exhaust branch pipe 9 varies depending on the exhaust cooling ability of the exhaust port 5 itself, so that the exhaust branch connected to the exhaust port 5 is the same as in the above embodiment. Between the pipe 9, the heat transfer inhibiting part according to the present invention is arranged. Even in such a configuration, a configuration corresponding to the heat transfer inhibiting portion according to the present invention, that is, an exhaust temperature discharged from the exhaust port during low load operation, is provided between the exhaust port 5 and the exhaust branch pipe 9. By applying the heat insulating member having the heat insulating property and the structure of the exhaust branch pipe shown in FIG. 11, the heat transfer (heat transfer Q15) from the entire exhaust branch pipe to the cooling adapter 10 is suppressed, and the connection flange 9c The thermal stress and the like can be suppressed in a well-balanced manner.

<Modification 3>
In the above-described embodiments, the heat insulating property of the portion 11b corresponding to the exhaust ports 5 # 1 and 5 # 4 in the heat insulating gasket 11 is set to be relatively small, but the exhaust temperature lowering is sufficiently suppressed. As long as it is not necessary, a heat insulating gasket may not be disposed in the portion 11b. In this case, the heat insulating gasket 11 is disposed only in the portion 11a corresponding to the exhaust ports 5 # 2, 5 # 3.

  In the present embodiment, attention is paid to the local exhaust cooling capacity at the connection portion where the exhaust port 5 # 1 having a relatively large exhaust cooling capacity is connected to the exhaust branch pipe 9. Below, the setting of the heat insulation of the heat insulation gasket 11 in this case is demonstrated. The upper part (a) of FIG. 12 shows a schematic configuration of the exhaust port 5 # 1. Here, in the exhaust port 5 # 1, apart from the bent portion 5d, a bent portion where the flow of the exhaust gas is bent (a “connected portion bent portion” according to the present invention) is formed in a portion connected to the exhaust branch pipe 9. It is formed to have an inner bend 5a # 1 with a relatively small bend radius and an outer bend 5b # 1 with a relatively large bend radius. The bent portion of the connection part is formed so that the exhaust port 5 # 1 is connected substantially perpendicularly to the end face of the exhaust branch pipe 9.

  By forming the connection part of the exhaust port 5 # 1 in this way, as described with reference to FIG. 7, when the internal combustion engine 1 is operated at a low load, the inner bent portion 5a # 1 is formed in the exhaust port 5 # 1. Is likely to be higher than the temperature of the outer bent portion 5b # 1. That is, at the time of low load operation of the internal combustion engine 1, a part of the connection part of the exhaust port 5 # 1 has a higher exhaust cooling capacity than the other part. Therefore, even if the exhaust is discharged from the same exhaust port 5 # 1, the exhaust temperature discharged through the vicinity of the inner bend 5a # 1 is the exhaust discharged through the vicinity of the outer bend 5b # 1. It becomes lower than the temperature.

  Therefore, in consideration of the difference in the exhaust temperature in the same exhaust port 5 as described above, the partial heat insulating property of the heat insulating gasket 11 may be set. Specifically, as shown in the lower part (b) of FIG. 12, a predetermined heat insulating gasket 11 corresponding to the inner bent portion of the connection portion of the exhaust ports 5 # 1 and 5 # 4 having a relatively large exhaust cooling capacity. The heat insulating property of the part 11c is set lower than the heat insulating property of the predetermined part 11d of the heat insulating gasket 11 corresponding to the outer bent portion of the connecting part of the exhaust ports 5 # 1, 5 # 4. By setting the heat insulation in this way, it is possible to achieve a good balance between the suppression of heat transfer (heat transfer Q15) from the entire exhaust branch pipe to the cooling adapter 10 and the suppression of thermal stress and the like at the connection flange 9c.

  In addition, what is necessary is just to form the site | part corresponding to the exhaust ports 5 # 2 and 5 # 3 with relatively low exhaust cooling capacity in the said Example as the predetermined site | part 11a with high heat insulation similarly. At this time, the heat insulation of the predetermined part 11a is set higher than the heat insulation of the predetermined part 11b.

  In the above-described embodiments, focusing on the exhaust cooling capability of the exhaust port 5, the heat insulating property of the heat insulating gasket 11 is set according to the exhaust temperature discharged from the exhaust port 5. In this embodiment, the cylinder 2 is supplied from the intake passage (not shown) of the internal combustion engine 1, which is a structural factor of the internal combustion engine 1 that affects the exhaust temperature from the exhaust port 5, through the intake port 4. Focus on the structure of the intake passage that causes variations in the intake air amount. Generally, when the air-fuel ratio of the air-fuel mixture formed in the cylinder 2 becomes a relatively rich air-fuel ratio, the exhaust temperature tends to be lowered due to the latent heat of vaporization of the fuel component contained in the exhaust after combustion. There is. Therefore, as a structural factor of the internal combustion engine 1, when there is a cylinder 2 into which a smaller intake amount flows than other cylinders, the cylinder 2 has a steady air-fuel ratio on the rich side compared to the other cylinders. An air-fuel mixture is formed, and the exhaust temperature discharged from the exhaust port 5 of the cylinder 2 is relatively low.

  For example, as in the exhaust port 5 shown in FIG. 2, the inlet of the intake port 4 corresponding to each cylinder (the opening on the side connected to the intake branch pipe not shown) is substantially at the center of the arrangement of the cylinders 2. If formed so as to gather in the part, the intake ports 4 corresponding to the inner cylinders 2 # 2 and 2 # 3 are formed in a shape having a relatively small curvature, so that the intake air easily flows into the cylinders. . On the other hand, the intake ports 4 corresponding to the outer cylinders 2 # 1 and 2 # 4 are formed in a shape having a relatively large curvature, so that the intake air hardly flows into the cylinders. Due to the difference in the ease of the intake air flow, there is a steady variation in the air-fuel ratio formed in each cylinder, which is relatively different from the cylinder in which the exhaust temperature discharged from the exhaust port 5 is relatively high. There will be low cylinders. The heat insulating property of the heat insulating gasket 11 may be adjusted in consideration of the difference in exhaust temperature caused by the structure of the intake passage of the internal combustion engine 1.

  In this case, heat insulation of a predetermined portion of the heat insulation gasket 11 corresponding to the exhaust ports 5 # 1 and 5 # 4 of the cylinder 2 where the air-fuel ratio of the air-fuel mixture tends to become a relatively rich air-fuel ratio due to structural factors of the intake passage. The heat resistance is set lower than that of a predetermined portion of the heat insulating gasket 11 corresponding to the remaining exhaust ports 5 # 2 and 5 # 3.

  Further, as a structural factor of the intake passage that affects the air-fuel ratio in the cylinder 2, when the internal combustion engine 1 is provided with an EGR device, a structure that determines the ease with which the EGR gas flows into the cylinder. Can also be mentioned.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Spark plug 4 Intake port 5 Exhaust port 5d Bending part 8 Fuel injection valve 9 Exhaust branch pipe 9a Upstream exhaust branch pipe 9b Downstream exhaust branch pipe 9c Connection flange 9e Collecting part 10 Cooling adapter 11 Thermal insulation gasket 12 Exhaust pipe 20 Exhaust purification catalyst

Claims (7)

The exhaust pipes connected to each of the plurality of exhaust ports formed in the cylinder head corresponding to the plurality of cylinders, and the exhaust purification catalyst is disposed in the exhaust pipe downstream from the gathering portion of the exhaust branch pipes An exhaust cooling system for an internal combustion engine,
A cooling section for cooling the exhaust branch pipe or the exhaust port;
A heat transfer inhibition unit configured to inhibit heat transfer from the exhaust branch pipe downstream from the cooling location by the cooling unit to the cooling unit, and the heat transfer inhibition capability by the heat transfer inhibition unit is When the internal combustion engine is in a predetermined low load operation state, the higher the exhaust temperature discharged from the exhaust port toward the exhaust branch pipe, the greater the inhibition ability corresponding to the exhaust port. A heat transfer inhibition portion set to
An exhaust cooling system for an internal combustion engine. The plurality of exhaust ports include at least a first exhaust port having a relatively small curved portion or a linear shape, and a second exhaust port having a relatively large curved portion,
The exhaust temperature discharged from the first exhaust port in the predetermined low load operation state is higher than the exhaust temperature discharged from the second exhaust port in the predetermined low load operation state, and the heat transfer inhibiting unit Is configured such that the inhibition capability corresponding to the first exhaust port by the heat transfer inhibition portion is greater than the inhibition capability corresponding to the second exhaust port by the heat transfer inhibition portion.
An exhaust cooling system for an internal combustion engine according to claim 1. The second exhaust port has a connection portion bending portion different from the bending portion having a relatively large curvature at a connection portion with the exhaust branch pipe, and the connection portion bending portion has a relative bending radius. Have a small inner bend and an outer bend with a relatively large bend radius,
The temperature of the inner bent portion in the predetermined low load operation state is higher than the temperature of the outer bent portion in the predetermined low load operation state,
The inhibiting ability corresponding to the second exhaust port by the heat transfer inhibiting part is set corresponding to each of the inner bent part and the outer bent part, and the inhibiting ability corresponding to the outer bent part is It is set to be larger than the inhibition ability corresponding to the inner bend,
An exhaust cooling system for an internal combustion engine according to claim 2. The inhibition capability corresponding to the outer bent portion is set lower than the inhibition capability corresponding to the first exhaust port,
An exhaust cooling system for an internal combustion engine according to claim 3. The plurality of cylinders are a first cylinder and a second cylinder configured to have different intake air amounts supplied from an intake passage, and the air-fuel ratio in the cylinders is relatively low in the predetermined low-load operation state. Including at least a first cylinder having a lean air-fuel ratio and a second cylinder having a relatively rich air-fuel ratio in the cylinder,
The exhaust temperature discharged from the first exhaust port corresponding to the first cylinder in the predetermined low load operation state is discharged from the second exhaust port corresponding to the second cylinder in the predetermined low load operation state. And the heat transfer inhibition portion has an inhibition capability corresponding to the first exhaust port by the heat transfer inhibition portion than an inhibition capability corresponding to the second exhaust port by the heat transfer inhibition portion. Configured to grow,
An exhaust cooling system for an internal combustion engine according to claim 1. The cooling unit is a cooling adapter that cools a part of the exhaust branch pipe, and the cooling adapter is connected to the other part of the exhaust branch pipe located on the upstream side of the collective part,
The heat transfer inhibiting portion includes an end face of the cooling adapter on a side to which the other part of the exhaust branch pipe is connected, a flange on the other part of the exhaust branch pipe on a side connected to the cooling adapter, and the cooling adapter. A gasket disposed between the end surface of the exhaust pipe and the flange, and is formed in at least one of predetermined portions from the flange to the gathering portion in the other part of the exhaust branch pipe.
An exhaust cooling system for an internal combustion engine according to any one of claims 1 to 5. The cooling unit is a cooling device that cools the exhaust port,
The heat transfer inhibiting portion includes a connection part of the cylinder head to which the exhaust branch pipe is connected, a flange of the exhaust branch pipe on a side connected to the cylinder head, and a gap between the connection part and the flange. A gasket to be disposed, formed in at least one of the predetermined portions from the flange to the gathering portion in the exhaust branch pipe;
An exhaust cooling system for an internal combustion engine according to any one of claims 1 to 5.

Images