JP2021032098A - Exhaust structure for internal combustion engine - Google Patents

Abstract

To increase specific power of an internal combustion engine while ensuring catalyst warming-up property.SOLUTION: An exhaust structure 1 includes: a cylinder head 2 formed with an exhaust manifold EM; and a swing heat-shielding film S formed at a wall surface of an exhaust passage of the exhaust manifold EM.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust structure of an internal combustion engine.

Patent Document 1 discloses an adiabatic exhaust port formed by casting on a cylinder head.

Jikkai Sho 59-154839

In the technique of Patent Document 1, while the heat insulation of the adiabatic exhaust port promotes catalyst warm-up, the increase in the exhaust temperature may reduce the maximum output with respect to the weight and external dimensions of the internal combustion engine, that is, the specific output of the internal combustion engine. is there.

The present invention has been made in view of such a problem, and an object of the present invention is to improve the specific output of an internal combustion engine while ensuring catalyst warmth.

The exhaust structure of an internal combustion engine according to an embodiment of the present invention has an exhaust port with a water jacket and an exhaust manifold, and has a lower thermal conductivity and a lower heat capacity on the wall surface of each of the exhaust port and the exhaust passage of the exhaust manifold than the base material of the wall surface. The heat shield film is formed.

The exhaust structure of an internal combustion engine according to another aspect of the present invention has a cylinder head in which a water jacket and an exhaust manifold are formed, and has a lower thermal conductivity and a lower heat capacity on the wall surface of the exhaust passage of the exhaust manifold than the base material of the wall surface. The structure is such that a heat shield film is formed.

According to these aspects, since the heat shield film has a lower thermal conductivity than the base material, it is difficult for heat to be transferred from the gas in the exhaust passage to the cylinder head, so that the catalyst warmth can be ensured. Further, according to these aspects, since the heat shield film has a lower heat capacity than the base material, the surface temperature of the heat shield film easily follows the gas temperature of the exhaust passage. At this time, heat is transferred from the high-temperature gas in the exhaust passage to the cylinder head, so that the exhaust cooling effect can be enhanced at the time of output as compared with the case where the exhaust passage is insulated with a heat insulating material, for example. Therefore, according to these aspects, it is possible to improve the specific output of the internal combustion engine while ensuring the catalyst warm-up property.

It is a schematic block diagram of the exhaust structure of the internal combustion engine which concerns on embodiment. It is a figure explaining the temperature state of the peripheral part of the exhaust passage wall surface. It is a figure which shows the change of the surface temperature of a swing heat shield film according to a crank angle. It is a figure which shows the temperature state of the peripheral part of the exhaust passage wall surface with a comparative example. It is explanatory drawing of the exhaust cooling effect of the swing heat shield film according to the surface enlarged shape.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram of an exhaust structure (hereinafter, simply referred to as an exhaust structure) 1 of an internal combustion engine. The exhaust structure 1 has a cylinder head 2. In the present embodiment, the cylinder head 2 is for an in-line 3-cylinder internal combustion engine, and has two opening INs for each cylinder. A water jacket WJ and an exhaust manifold EM are formed on the cylinder head 2. The water jacket WJ is provided around the exhaust manifold EM, and the cylinder head 2 is cooled by the coolant flowing through the water jacket WJ.

The exhaust manifold EM branches from the end opening OUT of the cylinder head 2 toward each cylinder, and the portion branched toward each cylinder is branched and connected to the opening IN to the corresponding cylinder. Such an exhaust manifold EM also serves as an exhaust port for each cylinder, and the cylinder head 2 is a cylinder head integrated with an exhaust manifold. In the present embodiment, the base material of the cylinder head 2 is an aluminum alloy, and the temperature of the cylinder head 2 is required to be suppressed to a temperature equal to or lower than the allowable temperature LMT during engine operation. It can also be understood that the exhaust manifold EM is composed of an exhaust port with a water jacket WJ and an exhaust manifold.

A swing heat shield film S is formed on the wall surface of the exhaust passage of the exhaust manifold EM. The swing heat shield film S is a film having a lower thermal conductivity and a lower heat capacity than the base material of the wall surface of the exhaust manifold EM, and therefore the base material of the cylinder head 2, and has a heat insulating performance, but can keep the gas temperature in the exhaust passage. It has the property that the surface temperature of the film follows. The heat capacity is, for example, the heat capacity per unit volume.

The swing heat shield film S is formed, for example, by anodizing the wall surface of the exhaust passage and then performing a hole sealing treatment using a silica-based coating liquid. As a result of the swing heat shield film S having a porous structure by anodization treatment, it is formed in a film having a lower thermal conductivity and a lower heat capacity than the base material, and the heat insulating property is improved by the sealing treatment using a coating liquid containing silica. It is planned.

FIG. 2 is a diagram illustrating a temperature state around the wall surface of the exhaust passage of the exhaust manifold EM. FIG. 2 shows the temperature state around the wall surface of the exhaust passage in accordance with the change in gas temperature according to the crank angle. The temperature TH is the temperature around the wall surface of the exhaust passage when the gas temperature is the highest in one combustion cycle, and the temperature TL is the temperature around the wall surface of the exhaust passage when the gas temperature is the lowest in one combustion cycle. is there. Both the temperature TH and the temperature TL are the temperatures at the time of the exhaust process of a certain cylinder.

When the gas temperature of the exhaust passage is high, the swing heat shield film S forms a temperature gradient in which the temperature TH rises from the cylinder head 2 side toward the exhaust passage side by following the gas temperature of the exhaust passage. Will be done. In the cylinder head 2, the temperature TH gradually increases from the water jacket WJ side toward the swing heat shield film S side, that is, the exhaust passage side. In the exhaust passage, the gas is cooled through the swing heat shield film S. As a result, in the exhaust passage, the temperature TH becomes lower as it approaches the swing heat shield film S. As a result, the exhaust cooling effect indicated by the lowered temperature D can be obtained.

When the gas temperature in the exhaust passage is low, the surface temperature of the swing heat shield film S follows the gas temperature in the exhaust passage, so that the surface temperature is lower than when the gas temperature in the exhaust passage is high. In the cylinder head 2, the temperature TL is the same as the temperature TH. Result In this example, the temperature TL of the exhaust passage is lower than that of the cylinder head 2. Therefore, in the exhaust passage, the gas receives heat through the swing heat shield film S, and the closer to the swing heat shield film S, the higher the temperature TL. In the swing heat shield film S, the temperature TL is substantially constant.

As the temperature around the wall surface of the exhaust passage changes in this way, the surface temperature of the swing heat shield film S changes with the temperature swing SW. The temperature swing SW is the range of change in the surface temperature of the exhaust passage during engine operation, and is, for example, the range of change in the surface temperature of the exhaust passage in one combustion cycle. Comparing the case where the swing heat shield film S is provided and the case where the swing heat shield film S is not provided, the temperature swing SW is different as follows.

FIG. 3 is a diagram showing changes in the surface temperature of the swing heat shield film S according to the crank angle. The broken line shows a comparative example. A comparative example shows a case where the swing heat shield film S is not provided, that is, a case where the base material of the cylinder head 2 constitutes the surface of the exhaust passage.

In the case of the comparative example, since the swing heat shield film S is not provided, the surface temperature of the exhaust passage wall surface is greatly affected by the cooling by the coolant. Therefore, the surface temperature does not rise significantly even if the gas temperature rises. In the case of the present embodiment, since the swing heat shield film S having the heat insulating performance is provided, the influence of the cooling liquid on the surface temperature of the wall surface of the exhaust passage is suppressed. Therefore, as the gas temperature rises, the surface temperature also rises significantly. As a result, the temperature swing SW in the case of the present embodiment is larger than that in the case of the comparative example.

The temperature swing SW has a temperature rise range of 200 ° C. or less from the state where the surface temperature is the lowest in one combustion cycle. The surface temperature is most lowered in, for example, the intake process due to the lowering of the physical temperature itself of the exhaust manifold EM due to the cooling liquid. The temperature swing SW can be set to a temperature rise range of 200 ° C. or lower by setting, for example, the surface area of the swing heat shield film S, the thermal conductivity of the swing heat shield film S, or the heat capacity. By suppressing the temperature swing SW to 200 ° C. or lower, a high exhaust cooling effect can be obtained, and the cylinder head 2 can be protected. This will be described later.

FIG. 4 is a diagram showing the temperature state around the wall surface of the exhaust passage together with a comparative example. In FIG. 4, the temperature state at the time of catalyst warm-up and the temperature state at the time of output, that is, when there is an acceleration request are shown side by side with the temperature on the vertical axis common. At the time of output, the excess air ratio λ is set to 1 to improve exhaust emissions. The temperature TH1 and the temperature TH2 indicate the temperature TH in the case of the comparative example.

The temperature TH1 corresponds to the first comparative example. The first comparative example shows a case where a heat insulating material having a higher heat insulating property than the swing heat insulating film S is provided on the wall surface of the exhaust passage of the exhaust manifold EM. In this case, the surface temperature at the time of warming up the catalyst and at the time of output is lower than the temperature TH shown in the case of this embodiment. In other words, in the case of the present embodiment, the surface temperature is higher than in the case of the first comparative example.

When the catalyst is warmed up, the gas temperature is lower than when it is output. Therefore, the amount of heat transfer from the gas to the wall surface of the exhaust passage is smaller than that at the time of output, and the temperature difference between the gas temperature and the surface temperature is also smaller than at the time of output. Therefore, in the case of the present embodiment represented by the temperature TH, the surface temperature is higher than that in the case of the first comparative example represented by the temperature TH1, but the catalyst warm-up property is sufficiently ensured.

At the time of output, the gas temperature is higher than that at the time of warming up the catalyst. Therefore, the amount of heat transfer from the gas to the wall surface of the exhaust passage is larger than that during the catalyst warm-up, and the temperature difference between the gas temperature and the surface temperature is also larger than that during the catalyst warm-up. Therefore, in the case of the present embodiment represented by the temperature TH1, although the surface temperature is higher than that in the case of the first comparative example represented by the temperature TH1, a sufficient exhaust cooling effect can be obtained at the time of output. Therefore, in the case of the present embodiment, both the catalyst warm-up property and the exhaust cooling effect at the time of output can be achieved at the same time.

In the cylinder head 2 using an aluminum alloy as the base material, the temperature swing SW is suppressed to 200 ° C. or lower as described above. As a result, the surface temperature rises only within the range of 200 ° C. or lower from the lowest state in one combustion cycle, regardless of whether the catalyst is warmed up or output. Therefore, a high exhaust cooling effect can be obtained at the time of output, and as a result of maintaining the surface temperature at a temperature lower than the allowable temperature LMT of the base material of the cylinder head 2, the temperature of the cylinder head 2 is also maintained at a temperature lower than the allowable temperature LMT. Will be done.

The temperature TH2 corresponds to the second comparative example. The second comparative example shows a case where the cylinder head 2 is deformed into a combination of a cylinder head in which a water jacket WJ and an exhaust port are formed, and an exhaust manifold connected to the exhaust port. In the second comparative example, the same heat insulating material as in the first comparative example is provided on the wall surface of each of the exhaust port and the exhaust passage of the exhaust manifold, but the water jacket WJ does not exist around the exhaust manifold.

In the second comparative example, the temperature TH2 at the time of warming up the catalyst indicates the temperature TH21 of the wall surface of the exhaust passage of the exhaust port. The temperature TH21 is the same as the temperature TH1. This is because the wall surface of the exhaust passage is insulated as in the first comparative example.

In the second comparative example, the temperature TH2 at the time of output indicates the temperature TH22 of the exhaust passage wall surface of the exhaust manifold. At the time of output, the temperature TH22, that is, the surface temperature of the exhaust passage in the exhaust manifold is significantly increased, and the temperature difference between the gas temperature and the surface temperature is also significantly reduced. As a result, the exhaust cooling effect is significantly reduced.

In the second comparative example, in the cylinder head provided with the water jacket WJ, the surface area of the exhaust passage wall surface is smaller than that in the case of the first comparative example, and this causes the case of the first comparative example. It can be said that the exhaust cooling effect is less than that. Therefore, it can be said that the exhaust cooling effect can be improved by increasing the surface area of the exhaust passage wall surface provided around the water jacket WJ.

Such an increase in the surface area can be performed by increasing the exhaust passage length of the cylinder head in the second comparative example, or by attaching the exhaust manifold in the second comparative example to the water jacket WJ. By attaching the exhaust manifold in the second comparative example with a water jacket WJ, the physical temperature itself can be lowered. The surface area may be increased by forming, for example, dimples or the like.

The improvement of the exhaust cooling effect by increasing the surface area is the same when the swing heat shield film S is provided on the wall surface of the exhaust passage instead of the heat insulating material, and the exhaust cooling effect when the swing heat shield film S is provided is heat insulating. Compared with the case where the material is provided, it is as follows.

FIG. 5 is an explanatory diagram of the exhaust cooling effect of the swing heat shield film S according to the surface enlarged shape. FIG. 5 shows a case where the exhaust passage, which is longer than the reference point P1 described later, has an enlarged surface shape. The vertical axis indicates the length of the exhaust passage provided around the water jacket WJ. The horizontal axis shows the heat transfer coefficient ratio from the gas to the wall surface of the exhaust passage. The heat transfer coefficient ratio indicates the ratio with the heat transfer coefficient at the reference point P1 on the line BASE.

The line BASE indicates a case where the swing heat shield film S is not provided, and therefore there is no exhaust cooling effect by the swing heat shield film S. The line BASE is generally located on the contour line of the gas temperature, and the gas temperature becomes lower as the exhaust passage length is longer and the heat transfer coefficient ratio is higher. The reference point P1 indicates a case where the exhaust passage length is a reference, that is, a case where the exhaust passage length is the minimum that can form an exhaust manifold in the cylinder head without causing an excessive flow loss. The case where the aluminum alloy used in a typical cylinder head has a thermal conductivity is shown. Lines TG1, line TG2, and line TG3 show, in this order, a case where the gas temperature can be lowered by approximately -10 ° C, -20 ° C, and -30 ° C at the time of output as compared with the case of the base indicated by the line BASE. ..

The line B shows the case of the first comparative example described above, that is, the case where the heat insulating material is provided on the wall surface of the exhaust passage. As shown by line B, if the exhaust passage length is longer than the reference point P1, the heat transfer coefficient ratio decreases, but line B is partially on the side where the gas temperature is lower than the line BASE with the same exhaust passage length. Located in. Therefore, even in this case, it can be seen that the gas temperature can be lowered by increasing the exhaust passage length as compared with the case of the base indicated by the line BASE. In this case, it can be seen that the increase in the exhaust passage length from the reference point P1 makes it possible to lower the gas temperature on the side where the gas temperature is higher than the line TG1, that is, to a degree smaller than −10 ° C.

Line A shows the case of this embodiment. In the case of the present embodiment, it can be seen that the gas temperature can be lowered with the same exhaust passage length as compared with the case of the base shown by the line BASE and the case of the first comparative example shown by the line B. That is, when the exhaust passage length is similarly lengthened, in the case of the present embodiment, the heat transfer coefficient ratio does not decrease as compared with the case of the base or the case of the first comparative example, so that the gas temperature can be further reduced. become.

In the case of the present embodiment, it can be seen that the gas temperature can be lowered on the side where the gas temperature is slightly lower than the line TG3 by increasing the exhaust passage length from the reference point P1. That is, in the case of this embodiment, it can be seen that the gas temperature can be lowered by about −30 ° C. The point P2 on the line A is the best point, and the exhaust cooling effect at the time of output is high due to the increase in the exhaust passage length from the reference point P1, and the heat insulating property is higher than that of the base indicated by the line BASE. ing.

Next, the main effects of the present embodiment will be described.

The exhaust structure 1 has an exhaust port with a water jacket WJ and an exhaust manifold EM as an exhaust manifold, and a swing heat shield is provided on the wall surface of the exhaust manifold EM as the wall surface of each of the exhaust port and the exhaust passage of the exhaust manifold. The structure is such that the film S is formed.

The exhaust structure 1 has a cylinder head 2 on which the exhaust manifold EM is formed, and a swing heat shield film S is formed on the wall surface of the exhaust passage of the exhaust manifold EM.

According to these configurations, since the swing heat shield film S has a lower thermal conductivity than the base material of the exhaust passage wall surface, it becomes difficult for heat to be transferred from the gas in the exhaust passage to the cylinder head 2, so that the catalyst warm-up property is achieved. Can be secured. Further, according to these configurations, since the swing heat shield film S has a lower heat capacity than the base material, the surface temperature of the swing heat shield film S is higher than that in the case where the exhaust passage is insulated with a heat insulating material, for example. It becomes easier to follow the gas temperature of. At this time, heat is transferred to the cylinder head 2 from the high-temperature gas in the exhaust passage, so that the exhaust cooling effect can be enhanced at the time of output. Therefore, according to these aspects, it is possible to improve the specific output of the internal combustion engine while ensuring the catalyst warm-up property.

In the exhaust structure 1, the exhaust passage on which the swing heat shield film S is formed has a surface-enlarged shape due to the elongated exhaust passage. According to such a configuration, it is possible to further enhance the exhaust cooling effect at the time of output.

In the exhaust structure 1, the swing heat shield film S has a temperature swing SW of 200 ° C. or lower during engine operation. According to such a configuration, it is possible to obtain a high exhaust cooling effect by minimizing the increase in gas temperature in the exhaust passage.

Although the embodiments of the present invention have been described above, the above embodiments are only a part of the application examples of the present invention, and the technical scope of the present invention is limited to the specific configurations of the above embodiments. Absent.

For example, in the above-described embodiment, the case where the exhaust manifold EM constitutes the exhaust port with the water jacket WJ and the exhaust manifold has been described. However, the exhaust port and the exhaust manifold with the water jacket WJ are composed of a cylinder head in which the water jacket WJ and the exhaust port are formed, and an exhaust manifold connected to the exhaust port and having the water jacket WJ. May be done.

1 Exhaust structure 2 Cylinder head EM exhaust manifold S Swing heat shield film WJ water jacket

Claims (4)

It has an exhaust port with a water jacket and an exhaust manifold.
A heat shield film having a lower thermal conductivity and a lower heat capacity than the base material of the wall surface is formed on the wall surface of each of the exhaust port and the exhaust passage of the exhaust manifold.
The exhaust structure of the internal combustion engine is characterized by this. It has a cylinder head with a water jacket and an exhaust manifold formed on it.
A heat shield film having a lower thermal conductivity and a lower heat capacity than the base material of the wall surface is formed on the wall surface of the exhaust passage of the exhaust manifold.
The exhaust structure of the internal combustion engine is characterized by this. The exhaust structure of the internal combustion engine according to claim 1 or 2.
The exhaust passage on which the heat shield film is formed has a surface enlarged shape.
The exhaust structure of the internal combustion engine is characterized by this. The exhaust structure of the internal combustion engine according to any one of claims 1 to 3.
The heat shield film has a change range of surface temperature of 200 ° C. or less during engine operation.
The exhaust structure of the internal combustion engine is characterized by this.

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