JP2005207277A - Exhaust cooling system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration of emission at the time of cold start with regard to an exhaust system of a multi-cylinder internal combustion engine wherein a single exhaust passage is formed with the assembled exhaust passages formed independently on respective cylinders, in a cooling system for the internal combustion engine wherein a communicating part for communicating the exhaust passages formed independently on the respective cylinders with each other is separately provided. <P>SOLUTION: The exhaust cooling system for the internal combustion engine, having a plurality of nozzle parts 14a-14d with ends on one side connected to the exhaust passages provided on the respective cylinders of the internal combustion engine, and a communicating pipe 15 for communicating the nozzle parts 14a-14d with each other by connecting the other ends of the nozzle parts 14a-14d thereto, has recessed and projecting parts 15a for increasing surface area of an inner wall surface of the communicating pipe 15. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  The exhaust port of each cylinder in a multi-cylinder internal combustion engine is connected to an exhaust manifold to form an independent exhaust passage for each cylinder. Further, the exhaust passages for each cylinder gather to form a single exhaust passage. In an exhaust system of an internal combustion engine, a technique is known in which a communication passage that connects the exhaust passages of each cylinder is separately provided (see, for example, Patent Document 1).

  The above-described technique aims to reduce the temperature of the exhaust gas by once introducing exhaust gas from an internal combustion engine into the communication passage and dissipating exhaust heat in the communication passage. With this prior art, the temperature of the exhaust gas passing through the exhaust purification catalyst provided in the exhaust passage of the internal combustion engine can be lowered, particularly when the operating state of the internal combustion engine is a high load and high rotational speed, An excessive temperature rise can be suppressed. As a result, exhaust purification by the exhaust purification catalyst is possible even in an operating state with a high load and a high rotational speed, and emissions can be reduced.

However, in the above-described prior art, when the internal combustion engine is cold started, the exhaust gas temperature is conversely lowered, so that the activation of the exhaust gas purification catalyst is delayed and the emission may be deteriorated. Further, in a specific operating state of the internal combustion engine, there is a case where interference of exhaust pulsation occurs and the engine output decreases.
Japanese Utility Model Publication No. 63-162959 Japanese Utility Model Publication No. 1-99926 Japanese Patent Laid-Open No. 7-238827

  According to the present invention, an exhaust passage for each cylinder is further communicated with an exhaust system of a multi-cylinder internal combustion engine in which exhaust passages formed independently for each cylinder are gathered to form a single exhaust passage. It is an object of the present invention to provide a technique capable of suppressing deterioration of emissions during cold start in an exhaust cooling system for an internal combustion engine in which a communication portion is separately provided.

To achieve the above object, the present invention provides a plurality of nozzle portions having one end connected to an exhaust passage provided for each of a plurality of cylinders in an internal combustion engine,
By connecting the other ends of the plurality of nozzle portions, the nozzle portions communicate with each other, and a communication portion that makes the exhaust in the exhaust passage compatible, and
An exhaust cooling system for an internal combustion engine comprising:
The communication part has an uneven part that increases the surface area of the inner wall surface of the communication part.

Here, at the time of cold start of the internal combustion engine, the pulsation of the exhaust discharged from each cylinder of the internal combustion engine is relatively small. Therefore, the amount of the exhaust discharged from each cylinder of the internal combustion engine during the cold start passes through the nozzle portion and reaches the communication portion is relatively small. On the other hand, after the internal combustion engine is warmed up, the pulsation of the exhaust gas discharged from each cylinder of the internal combustion engine is large particularly in an operating state at a high load and a high rotational speed. Therefore, in this case, most of the exhaust discharged from each cylinder of the internal combustion engine passes through the nozzle portion and circulates in the communication portion. Further, a part of the cylinder may reach a cylinder corresponding to the nozzle portion via another nozzle portion.

  That is, a plurality of nozzle portions connected at one end to an exhaust passage provided for each of the plurality of cylinders, and a communication portion that connects the nozzle portions to each other by connecting the other end of the plurality of nozzle portions, When the internal combustion engine is cold started, most of the exhaust heat discharged from each cylinder is dissipated from the wall surface of the nozzle portion. On the other hand, most of the exhaust heat is dissipated from the wall surface of the communication portion after the internal combustion engine is warmed up, particularly in an operating state with a high load and a high rotational speed.

  In the present invention, the heat dissipation efficiency of the exhaust gas from the communication portion is improved by providing the communication portion with an uneven portion that increases the surface area of the inner wall surface of the communication portion. In general, the tube diameter of the communication portion is often set larger than the tube diameter of the nozzle portion, and conventionally, the heat dissipation efficiency of the exhaust gas from the nozzle portion is higher than that of the nozzle portion. It can be said that the heat dissipation efficiency from the communication part was better. Therefore, in other words, in the present invention, the difference between the heat dissipation efficiency of the exhaust from the nozzle portion and the heat dissipation efficiency of the exhaust from the communication portion is further increased.

  According to this, at the time of cold start of the internal combustion engine, since the amount of exhaust reaching the communication part is small among the exhaust discharged from the internal combustion engine, the amount of exhaust heat dissipated as a whole can be suppressed. . On the other hand, after the internal combustion engine is warmed up, particularly in a state of high load and high rotation speed, a large part of the exhaust discharged from the internal combustion engine reaches the communication part and flows through the communication part. The part can dissipate exhaust heat more efficiently.

  As a result, when the internal combustion engine is cold-started, it is possible to prevent the exhaust discharged from each cylinder of the internal combustion engine from being cooled in the communication portion. Thereby, the fall of exhaust temperature can be suppressed and the delay of activation of an exhaust purification catalyst can be suppressed. On the other hand, after the internal combustion engine is warmed up, particularly in an operating state with a high load and a high rotational speed, the exhaust discharged from each cylinder of the internal combustion engine can be cooled more efficiently in the communication portion. As a result, it is possible to more reliably suppress the excessive temperature rise of the exhaust purification catalyst when the internal combustion engine is in a high-load high-speed state.

  In the above, the smaller the cross-sectional area of the nozzle portion, the more difficult it is for the exhaust discharged from the cylinder of the internal combustion engine to pass through the nozzle portion. Further, the longer the nozzle portion is, the more difficult it is for the exhaust discharged from the cylinder of the internal combustion engine to pass through the nozzle portion. Accordingly, the cross-sectional area and length of the nozzle part are set on condition that the exhaust discharged from the cylinder hardly reaches the communication part depending on the exhaust pulsation during the cold start of the internal combustion engine. desirable. As a result, when the internal combustion engine is cold-started, it is possible to more reliably suppress a decrease in the exhaust gas temperature and to suppress a delay in the activation of the exhaust gas purification catalyst.

  At that time, it is desirable to make the surface area of the nozzle part as small as possible. By doing so, it is possible to more effectively suppress the dissipation of exhaust heat from the inner wall surface of the nozzle portion at the time of cold start of the internal combustion engine, and it is possible to more reliably suppress the decrease in the exhaust temperature. . A circular shape can be exemplified as the cross-sectional shape of the nozzle portion for reducing the surface area of the nozzle portion. Further, it is desirable to form the nozzle portion as linear as possible. By doing so, when the distance between the communication portion and the cylinder of the internal combustion engine is the same, the surface area of the entire nozzle portion can be further reduced.

Further, it is desirable not to provide a cooling water passage for the internal combustion engine in the vicinity of the nozzle portion. By doing so, it is possible to suppress the heat of the exhaust gas in the nozzle portion from being taken away by the cooling water, and more reliably suppress the exhaust temperature of the internal combustion engine from being lowered during the cold start of the internal combustion engine. be able to.

  Conversely, it is desirable that the cross-sectional area of the communicating portion in the present invention be as large as possible. As a result, the surface area of the inner surface of the communication portion can be increased, and the exhaust heat of the exhaust discharged from each cylinder of the internal combustion engine can be radiated more efficiently. As a result, the temperature of the exhaust can be reduced more efficiently.

  Further, in the present invention, the shape of the communication part is a tube having a constant cross-sectional shape, and the uneven part is an uneven part provided on the outline of the cross section, and the length of the communication part. It should have a certain shape in the direction. In this way, the concavo-convex part in the communication part can be easily formed by molding or drilling, and the productivity of the communication part can be improved and the cost can be reduced.

  Here, an exhaust cooling system that is a premise of the present invention, that is, a plurality of nozzle portions connected at one end to an exhaust passage provided for each cylinder, and a communication portion connected at the other end of the plurality of nozzle portions In an exhaust cooling system for an internal combustion engine having the above, exhaust pulsation interference may occur. This exhaust pulsation interference refers to the following phenomenon. For example, in a predetermined operating state of the internal combustion engine, exhaust discharged from a cylinder in an exhaust stroke passes through a nozzle part connected to an exhaust passage provided independently for the cylinder and a communication part, and When the cylinder that is in the intake stroke at that time reaches the cylinder through the nozzle corresponding to the cylinder, the intake stroke is in a period in which the valve opening period of the intake valve and the valve opening period of the exhaust valve overlap. May be introduced from an exhaust valve into a certain cylinder. Thus, the exhaust pulsation interference is that the exhaust pulsation of one cylinder affects the other cylinders. When this exhaust pulsation interference occurs, the ratio of fresh air in the cylinders in the intake stroke decreases, and as a result, the engine output may decrease.

  Therefore, in the present invention, the shape of the communication portion is a tube having a circular cross section, and the uneven portion is formed by changing the diameter of the circular cross section according to the position in the length direction of the communication portion. You may make it do. By doing so, excessively active circulation of the exhaust gas in the communication part can be suppressed, and the exhaust gas flowing in from one nozzle part is inadvertently discharged from the communication part to another nozzle part. Can be suppressed.

  As a result, the activation delay of the exhaust purification catalyst at the time of cold start of the internal combustion engine can be suppressed, and the excessive temperature rise of the exhaust purification catalyst can be suppressed in the operating state of the internal combustion engine at a high load and high rotation speed. In addition, the above-described exhaust pulsation interference can also be suppressed.

  In addition, the shape of the communication part for obtaining the same effect is a tube having the circular cross section as described above, and the uneven part has a diameter of the circular cross section depending on the position in the length direction of the communication part. It is not restricted to what is formed by changing. That is, the uneven portion provided in the communication portion may be in a shape that can suppress excessively active circulation of exhaust gas in the communication portion. For example, the communication portion is a tube having a circular cross section, and the uneven portion is It may be such that protrusions are distributed on the inner wall surface.

  In the present invention, it is desirable to provide a cooling water passage in the vicinity of the communication portion. In this way, the exhaust gas of the internal combustion engine can be cooled more efficiently in the operating state of the internal combustion engine at a high load and a high rotational speed.

In the present invention, the inner wall surface of the nozzle portion may be formed of a material having low thermal conductivity, and the wall surface of the communication portion may be formed of a material having high thermal conductivity. Good. Furthermore, both may be performed. As a result, the heat dissipation efficiency of the exhaust heat from the nozzle portion can be further reduced, and the heat dissipation efficiency of the exhaust heat from the communication portion can be further improved. As a result, it is possible to more reliably suppress a decrease in exhaust gas temperature during cold start of the internal combustion engine, and more efficiently exhaust the internal combustion engine after warming up the internal combustion engine, particularly in an operating state at a high load and high speed. Can be cooled to.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  In the present invention, in addition to the exhaust system of a multi-cylinder internal combustion engine in which exhaust passages formed independently for each cylinder are gathered to form a single exhaust passage, the exhaust passages for each cylinder are further connected to each other. In a cooling system for an internal combustion engine that is separately provided with a communication portion that communicates with each other, it is possible to suppress the deterioration of emissions during cold start.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its exhaust cooling system according to the present embodiment. An internal combustion engine 1 shown in FIG. 1 is a multi-cylinder diesel engine having four cylinders 2.

  An intake branch pipe 8 is connected to the internal combustion engine 1, and an upstream side of the intake branch pipe 8 is further connected to an intake pipe 9. On the other hand, an exhaust branch pipe 18 is connected to the internal combustion engine 1, and an exhaust pipe 19 is connected to the downstream side of the exhaust branch pipe 18. The exhaust pipe 19 is connected to a muffler (not shown) downstream.

  An exhaust purification catalyst 20 is disposed in the middle of the exhaust pipe 19. Examples of the exhaust purification catalyst 20 include hydrocarbon (HC), carbon monoxide contained in the exhaust when the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst 20 is a predetermined air-fuel ratio in the vicinity of the theoretical air-fuel ratio. (CO), a three-way catalyst for purifying nitrogen oxide (NOx), and when the air-fuel ratio of the exhaust gas flowing into the exhaust gas purification catalyst 20 is a lean air-fuel ratio, occludes nitrogen oxide (NOx) contained in the exhaust gas And a NOx storage reduction catalyst that reduces and purifies while releasing the stored nitrogen oxide (NOx) when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 20 is a stoichiometric air-fuel ratio or a rich air-fuel ratio, The selective reduction type NOx catalyst for reducing and purifying nitrogen oxide (NOx) in the exhaust when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 20 is in an oxygen excess state and a predetermined reducing agent is present, or the above Each Catalyst such as is used comprising a combination of catalysts suitable.

  Note that the exhaust purification catalyst 20 described above needs to be in an activated state by increasing the temperature of the exhaust purification catalyst 20 in order to exhibit its performance sufficiently. Therefore, if the exhaust gas is introduced into the exhaust gas purification catalyst 20 in a state where the exhaust gas purification catalyst 20 is not sufficiently activated, the exhaust gas is not sufficiently purified and the emission is deteriorated.

Further, one end of the nozzle portions 14 a to 14 d is connected to the exhaust port 30 of each cylinder 2. The other ends of the nozzle portions 14 a to 14 d are connected to the communication pipe 15. A part of the exhaust discharged from each cylinder 2 passes through the nozzle portions 14 a to 14 d and circulates in the communication pipe 15. At this time, exhaust heat is dissipated through the wall surface of the communication pipe 15. Further, the exhaust gas flowing into the communication pipe 15 is mixed with the low-temperature exhaust gas already stored in the exhaust pipe 15. By these actions, the temperature of the exhaust gas that passes through the nozzle portions 14 a to 14 d again and returns to the exhaust port 30 is lowered. As a result, the temperature of the exhaust gas introduced into the exhaust purification catalyst 20 can be lowered, and an excessive temperature rise of the exhaust purification catalyst 20 can be suppressed even in an operating state with a high load and a high rotational speed. The communication pipe 15 is a part that functions as a communication part in the present embodiment.

  Here, in FIG. 1, for ease of understanding, the nozzle portions 14 a to 14 d and the communication pipe 15 are depicted as being formed outside the internal combustion engine 1, but in this embodiment, the internal combustion engine It is assumed that it is formed in a cylinder head (not shown) in the engine 1. However, it goes without saying that the nozzle portions 14 a to 14 d and the communication pipe 15 may be formed outside the internal combustion engine 1.

  Moreover, the shape of the communication pipe 15 in the present embodiment is a tubular shape having the same cross-sectional shape in the direction of the arrow in FIG. In FIG. 2, the example of a cross-sectional shape at the time of seeing the communicating pipe 15 from the direction of the arrow is shown. In this embodiment, when the communication pipe 15 is viewed from the direction of the arrow, it is assumed that it has a cross-sectional shape as shown in FIG. As shown in FIG. 2A, by providing the communication pipe 15 with the concavo-convex portion 15 a, the surface area per unit length in the arrow direction of the communication pipe 15 can be increased, and the exhaust gas flowing through the communication pipe 15. The exhaust heat can be dissipated more efficiently.

  If the cross-sectional shape of the communication tube 15 is as shown in FIG. 2A and the cross-sectional shape is constant in the longitudinal direction of the communication tube 15 as in the present embodiment, In addition, the communication pipe 15 can be easily formed by drilling. In addition, when the cross-sectional shape at the time of seeing the communicating pipe 15 from the arrow direction is made as shown in FIGS. 2B to 2D, it is difficult to form the communicating pipe 15 by drilling. However, it can be easily formed by molding.

  In the above description, in consideration of workability, the communication pipe 15 is formed in a linear shape in the length direction of the communication pipe 15. However, it is not always necessary to form a straight line. By forming the communication pipe 15 in a curved shape, the surface area of the communication pipe 15 as a whole can be increased, and the exhaust heat of the exhaust gas flowing through the communication pipe 15 can be dissipated more efficiently.

  Next, the shape of the nozzle portions 14a to 14d in FIG. 1 is a tube having a circular cross section, and is formed linearly in the length direction. The diameters D and lengths L of the nozzle portions 14a to 14d are such that when the internal combustion engine 1 is idling, part of the exhaust discharged from each cylinder 2 of the internal combustion engine 1 is discharged from the exhaust port 30 to the nozzle portions 14a to 14d. In this case, the exhaust gas is set so as to satisfy the condition that the exhaust gas hardly reaches the communication pipe 15. At the same time, the diameters D and lengths L of the nozzle portions 14a to 14d are such that when the internal combustion engine is operating at a high load and high speed, a part of the exhaust discharged from each cylinder 2 of the internal combustion engine 1 is exhaust port. When the gas flows into the nozzle portions 14 a to 14 d from 30, it is set so as to satisfy the condition that most of the exhaust reaches the communication pipe 15 and flows through the communication pipe 15. The diameter D and the length L that satisfy both of the conditions described above are obtained experimentally.

  Here, the values of the diameters D of the nozzle portions 14a to 14d that satisfy the above conditions are often smaller than those that do not satisfy the above conditions. Moreover, since the cross-sectional shape of nozzle part 14a-14d is circular as above mentioned, the surface area of nozzle part 14a-14d per unit length is small compared with the case where it is another cross-sectional shape. . As a result, it can be said that the heat dissipation efficiency of the exhaust in the nozzle portions 14a to 14d is designed to be kept low. On the other hand, the communication pipe 15 is provided with the uneven portion 15a as described above, so that the heat dissipation efficiency is improved.

  Further, although not shown in FIG. 1, in the present embodiment, the cooling water passage for cooling the internal combustion engine 1 is provided mainly in the vicinity of the communication pipe 15 in the cylinder head. On the other hand, it is not broken in the vicinity of the nozzle portions 14a to 14d. This also acts to suppress the heat dissipation efficiency in the nozzle portions 14a to 14d and improve the heat dissipation efficiency in the nozzle portion 15.

  FIG. 3 is a diagram illustrating the operation of the nozzle portions 14 a to 14 d and the communication pipe 15. FIG. 3A is a diagram showing the flow of exhaust gas from the exhaust port 30 when the internal combustion engine 1 is cold-started, and FIG. 3B is a diagram showing a particularly high load and high rotational speed after the internal combustion engine 1 is warmed up. It is a figure which shows distribution | circulation of the exhaust_gas | exhaustion from the exhaust port 30 in a driving | running state.

  As shown in FIG. 3A, when the internal combustion engine 1 is cold started, the exhaust gas introduced into the nozzle portions 14 a to 14 d from the exhaust port 30 hardly reaches the inside of the communication pipe 15. Therefore, most of the exhaust from each cylinder 2 pulsates in the nozzle portions 14a to 14d. As a result, the exhaust heat of the exhaust from each cylinder 2 is dissipated only from the nozzle portions 14a to 14d in which the heat dissipation efficiency is suppressed as described above, so that the temperature drop of the exhaust is suppressed.

  On the other hand, as shown in FIG. 3B, most of the exhaust gas introduced from the exhaust port 30 to the nozzle portions 14a to 14d is communicated after the internal combustion engine is warmed up, particularly in an operating state at a high load and high speed. The inside of the tube 15 is reached. Then, it circulates in the communication pipe 15. Therefore, the exhaust heat of the exhaust from each cylinder 2 is dissipated from the inner wall of the communication pipe 15 having the heat dissipation efficiency improved by having the concavo-convex portion 15a as described above, so that the temperature drop of the exhaust is promoted. .

  As described above, in the present embodiment, when the internal combustion engine 1 is cold-started, the temperature drop of the exhaust gas is suppressed and the activation delay of the exhaust purification catalyst 20 can be suppressed. When the internal combustion engine 1 is operating at a high load and a high rotational speed, it is possible to suppress an excessive temperature rise of the exhaust purification catalyst 20.

  In FIG. 4, the front view and side view are shown about the other example of the uneven | corrugated | grooved part 15a of the communicating pipe 15 in a present Example. In FIG. 4A, the communication pipe 15 is formed in a shape in which cylinders having different diameters are alternately overlapped. That is, the uneven portion 15a is formed by the difference in the diameter of the cylinder. In this case, the exhaust heat of the exhaust gas introduced into the communication pipe 15 from the nozzle portions 14 a to 14 d is efficiently dissipated from the inner wall surface of the communication pipe 15 due to the uneven portion 15 a in the communication pipe 15.

  In addition to this, in the example shown in FIG. 4A, the concavo-convex portion 15 a is provided so as to form a wall in a direction perpendicular to the main exhaust flow direction in the communication pipe 15. Therefore, the uneven portion 15a can suppress the excessively active circulation of the exhaust gas in the communication pipe 15, and can suppress the exhaust gas flowing from one nozzle portion from flowing into another nozzle portion. As a result, it is possible to suppress the occurrence of exhaust pulsation interference in the specific operation state of the internal combustion engine 1.

  FIG. 4B shows another example of the uneven portion 15a of the communication pipe 15 in the present embodiment. In this example, an uneven portion 15 a is formed by providing an elliptical protrusion on the inner wall of the communication tube 15, thereby increasing the surface area of the inner wall of the communication tube 15. In this example as well, the elliptical protrusions suppress excessively active circulation of the exhaust gas in the communication pipe 15, so that the exhaust gas flowing from one nozzle part is prevented from flowing into another nozzle part. it can. As a result, it is possible to suppress the occurrence of exhaust pulsation interference in the specific operation state of the internal combustion engine 1.

  In the above embodiment, the example in which the present invention is applied to a multi-cylinder diesel engine has been described. However, the present invention may be applied to a gasoline engine.

  In the above embodiment, the communication pipe itself is hermetically sealed except for the connection portion with the nozzle portion, but the configuration of the communication portion in the present invention is not limited thereto. For example, a configuration in which a part of the communication unit has an opening to the outside and communicates with the atmosphere, or a configuration in which a valve for controlling connection between the communication unit and the outside is further included in the configuration.

1 is a diagram showing a schematic configuration of an internal combustion engine and an exhaust cooling system thereof according to the present invention. It is a figure which shows the example of the cross-sectional shape of the communicating pipe | tube in the Example of this invention. It is a figure explaining the effect | action of the exhaust cooling system in the Example of this invention. It is a figure shown about the other example of the uneven | corrugated | grooved part provided in the communicating pipe in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 8 ... Intake branch pipe 9 ... Intake pipe 14a, 14b, 14c, 14d ... Nozzle part 15 ... Communication pipe 15a ... Uneven part 18 ..Exhaust branch pipe 19 ... Exhaust pipe 20 ... Exhaust purification catalyst 30 ... Exhaust port D ... Nozzle part diameter L ... Nozzle part length

Claims (3)

A plurality of nozzle portions connected at one end to an exhaust passage provided for each of a plurality of cylinders in the internal combustion engine;
By connecting the other ends of the plurality of nozzle portions, the nozzle portions communicate with each other, and a communication portion that makes the exhaust in the exhaust passage compatible, and
An exhaust cooling system for an internal combustion engine comprising:
The exhaust cooling system for an internal combustion engine, wherein the communication portion has an uneven portion that increases a surface area of an inner wall surface of the communication portion.   The shape of the communication part is a tube having a constant cross-sectional shape, and the uneven part is an uneven part provided on the outline of the cross-section, and has a constant shape in the length direction of the communication part. The exhaust cooling system for an internal combustion engine according to claim 1.   The shape of the communication part is a tube having a circular cross section, and the uneven part is formed by changing the diameter of the circular cross section according to the position in the length direction of the communication part. Item 6. An exhaust cooling system for an internal combustion engine according to Item 1.

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