JP2003206736A - Structure of exhaust manifold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the noise of a specific frequency felt as displeasure for a driver among radiation noises from an exhaust manifold. <P>SOLUTION: The structure of exhaust manifold is characterized in that the manifold is composed of elastic components such as a SUS material, and a mass damper is provided at a low rigid region of side walls of the exhaust manifold or at the a region where vibration tends to generate due to an exhaust gas flow in the exhaust manifold having a plurality of independent exhaust passages used for an internal combustion engine. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a structure of an exhaust manifold used in an internal combustion engine.

[0002]

2. Description of the Related Art Generally, an internal combustion engine for a vehicle has a plurality of combustion chambers. In each combustion chamber, intake stroke, compression stroke,
The expansion stroke and the exhaust stroke are repeated. The combustion gas burned in the combustion chamber (hereinafter referred to as exhaust gas) is released from the combustion chamber to the exhaust manifold during the exhaust stroke. Therefore, since the exhaust gas is intermittently released from the internal combustion engine to the exhaust manifold, the exhaust gas flow in the exhaust passage becomes a pulsating flow. Since the discharged exhaust gas has a very high pressure, the side wall of the exhaust manifold is vibrated in combination with the pulsating flow to generate a radiant sound.

As a countermeasure against this radiated sound, there is an exhaust manifold structure provided with a sound insulating plate covering the exhaust manifold. Such an exhaust manifold structure has an excellent sound deadening effect and is used in many vehicles. However, the temperature of the exhaust manifold itself may rise due to the recent increase in the output of the internal combustion engine and the heat insulation effect of the sound insulation plate, which may reduce the reliability of the exhaust manifold. That is, although the exhaust manifold has a portion where welding is performed, thermal stress is concentrated on this welding joint, and there is a possibility that the welding joint may be distorted when the temperature becomes high.

As another measure, a method of increasing the thickness of the exhaust manifold can be considered. However, increasing the thickness of the exhaust manifold is not appropriate due to the following reasons.

The exhaust gas discharged from the combustion chamber passes through the exhaust manifold and flows into the exhaust gas purifying device installed in the exhaust passage. In the exhaust gas purification device, poisonous components of exhaust gas are detoxified by the catalytic action of platinum or the like.
Such a catalytic action is efficiently exhibited at a predetermined temperature (about 400 degrees) or higher. Therefore, when the temperature of the exhaust gas purification device is low, such as immediately after starting the internal combustion engine, it is necessary to raise the temperature of the exhaust gas purification device immediately. It is desirable to arrange it on the upstream side of the exhaust gas flow. However, even if the exhaust gas purification device is arranged at a position close to the internal combustion engine, as described above, when the plate thickness of the exhaust manifold that connects the internal combustion engine and the exhaust gas purification device is increased as a measure against radiation noise, Since the heat capacity of the exhaust manifold increases, heat is taken by the exhaust manifold before the exhaust gas purification device is warmed, which causes a problem that the warm-up performance of the exhaust gas purification device is not improved.

In recent years, in order to improve the warm-up performance of the exhaust gas purifying device as a measure against exhaust gas, the heat capacity of the exhaust manifold tends to be lowered. Therefore, S, which has a small heat capacity
An exhaust manifold consisting of US pipes and SUS plates is used. The exhaust manifold including the SUS pipe and the SUS plate is more likely to emit radiant sound than the conventional casting exhaust manifold. Further, as described above, in order to reduce the heat capacity of the exhaust manifold, there is a demand for thinning of the SUS pipe and the SUS plate, and it can be said that this tends to cause emission noise from the exhaust manifold more easily.

[0007]

The radiated sound emitted from the exhaust manifold includes sounds in the low frequency range to sounds in the high frequency range. Among the conventional technologies, the former technology does not suppress the emission of radiated sound from the exhaust manifold, but blocks the transmission of radiated sound from the exhaust manifold. The propagation of sound is blocked as a wide target. The latter technology suppresses the vibration of the exhaust manifold sidewalls and suppresses the generation of radiated sound from the exhaust manifold, which also suppresses the generation of sounds from low-frequency sounds to high-frequency sounds. To do.

Since these conventional techniques have a wide frequency range of sound to be the target of radiation noise countermeasures, in addition to the above-mentioned disadvantages, the former technique requires the design of a sound insulating plate suitable for the shape of each exhaust manifold. Therefore, the development cost and the component cost have increased. Further, in the latter technique, there is a problem that the weight of the exhaust manifold increases, however, unlike the conventional technique, it is not necessary to take measures against radiated sound even for a sound that does not feel uncomfortable for the driver.

[0009] Therefore, an object of the present invention is to reduce the sound of a specific frequency, which is uncomfortable for the driver, of the sound emitted from the exhaust manifold.

[0010]

According to a first aspect of the present invention, there is provided an exhaust manifold structure characterized in that a mass body is provided on an outer surface of the exhaust manifold.

According to a second aspect of the present invention, in an exhaust manifold having a plurality of independent exhaust passages, a mass body is provided on a side wall of the independent exhaust passage having the longest axial length among the independent exhaust passages. It is an exhaust manifold structure.
The invention according to claim 3 is an exhaust manifold having a plurality of independent exhaust passages, wherein a mass body is provided on a wall forming a collecting portion where the independent exhaust passages are assembled. is there.

According to a fourth aspect of the present invention, there is provided an exhaust manifold having an independent exhaust passage having a curved portion or a bent portion, wherein a mass body is provided at the curved portion or the bent portion. Is.

The invention of claim 5 is the invention of claims 1 to 4.
5. The mass body according to claim 1 is attached to a bracket having a linear expansion coefficient substantially the same as that of the exhaust manifold, and the bracket to which the mass body is attached is fixed to the outer surface of the exhaust manifold. Exhaust manifold structure.

[0014]

Next, with reference to FIG. 1 and FIG. 2, the mechanism by which a radiated sound is generated from the exhaust manifold 1 by the flow of exhaust gas will be described. Since the exhaust gas immediately after being discharged from the internal combustion engine has a high pressure, for example, when passing through the independent exhaust passage 3, the passage cross-sectional area of the independent exhaust passage 3 increases by a minute amount due to the pressure. Since the exhaust gas is intermittently discharged to the independent exhaust passage 3 as described above, at the next moment when the passage cross-sectional area of the independent exhaust passage 3 slightly increases, the exhaust gas flow disappears and the passage of the independent exhaust passage 3 is interrupted. The area returns to its original value due to the restoring force due to the elasticity of the SUS member forming the independent exhaust passage, and then becomes smaller by a small amount than the original passage cross-sectional area due to inertia. Then, the restoring force that causes the independent exhaust passage 3 to return to the original shape is generated. Then, the passage cross-sectional area of the independent exhaust passage 3 continues to increase and decrease until the exhaust gas flows into the independent exhaust passage 3 next. That is, the side wall of the independent exhaust passage 3 continues to vibrate. This is considered to be one of the causes of the radiated sound emitted from the exhaust manifold 1.

As another cause, as can be seen from FIG. 1, the independent exhaust passage 3 has a curved portion 22. When the high-pressure exhaust gas flow immediately after being discharged cannot smoothly flow through the curved portion 22 and collides with the inner wall 23 of the independent exhaust passage, the independent exhaust passage 3 is distorted due to the impact of the collision force. The independent exhaust passage 3 tends to return to its original shape due to the restoring force of the elasticity of the SUS material. The side wall of the independent exhaust passage 3 vibrates according to the same principle as described above. Since the next exhaust step is performed before this vibration is damped, the side wall of the independent exhaust passage 3 continues to vibrate. It is considered that the emission noise is generated from the exhaust manifold 1 due to these two causes.

The generation of radiated sound generated by these causes changes depending on the operating state of the internal combustion engine, the shapes of the independent exhaust passages 3 to 6, and the like. For example, the rotation speed of the internal combustion engine correlates with the discharge interval of the exhaust gas discharged into the independent exhaust passages 3 to 6. Therefore, if the rotation speed of the internal combustion engine is increased, the high-frequency radiation sound is increased and the low-frequency radiation is emitted. The sound is reduced. Further, since the shape of the independent exhaust passage correlates with the easiness of distortion of the independent exhaust passages 3 to 6 (if the distortion is easy, the restoring force for a unit distortion is small), the exhaust gas collides with the easily distorted portion, etc. The side wall vibrates and emits a radiant sound.

Therefore, according to the first aspect of the present invention, since the mass body is provided on the outer surface of the exhaust manifold, the vibration speed of the exhaust manifold side wall changes, and the radiated sound can be reduced. Further, as in the inventions of claims 2 to 3, by mounting the mass body on a portion of the side wall of the independent exhaust passage where vibration easily occurs (a portion where the restoring force per unit displacement amount is small), the emitted sound can be efficiently emitted. Occurrence can be suppressed. Further, as in the invention of claim 4, due to the relationship between the exhaust gas flow and the shape of the independent exhaust passage, by mounting the mass body on the side wall of the independent exhaust passage where vibration is likely to occur, radiated sound can be efficiently generated. Can be suppressed. That is, since the restoring force per unit displacement amount of the side wall is small in the part where the side wall is easily vibrated, the vibration speed of the side wall is reduced when the mass body is attached to the part, vibration is suppressed, and generation of radiated sound is suppressed. can do. Then, by adjusting the mass of the mass body, it is possible to selectively suppress the generation of the radiation sound of the specific frequency.

According to the fifth aspect of the present invention, since the thermal expansion of the exhaust manifold and the thermal expansion of the bracket to which the mass body is attached are substantially the same, excessive stress due to the difference in thermal expansion is caused at the joint between the exhaust manifold and the bracket. Is suppressed.
Also, because the mass body and the bracket are molded separately,
By adjusting the mass of the mass body, the mass manifold can be applied to exhaust manifolds of various shapes, so that the cost merit is large.

[0019]

1 is a top view of an exhaust manifold 1 attached to an internal combustion engine having four cylinders and an exhaust gas purification device 2 installed downstream thereof, and FIG. 2 is a front view thereof. The exhaust manifold 1 is composed of independent exhaust passages 3, 4, 5, 6 communicating with respective combustion chambers (not shown) of the internal combustion engine, and a collecting portion 7 in which the independent exhaust passages 3 to 6 are assembled. The independent exhaust passages 3 to 6 and the collecting portion 7 have a thickness 1.
It is manufactured by welding the joint part 10 of the upper part 8 and the lower part 9 made of a SUS plate of about 5 mm.

The mass damper 14 for reducing the radiated sound from the exhaust manifold 1 is fixed to the outer surface of the exhaust manifold 1 by welding. A cylinder head (not shown) of the internal combustion engine is provided at the upstream end of each of the independent exhaust passages 3 to 6.
A mounting flange 16 is provided for fastening with, and mounting bolt holes 12 are formed in the mounting flange 16. On the other hand, on the downstream side of the collecting portion 7 of the independent exhaust passages 3 to 6,
An exhaust gas purification device 2 is arranged.

The exhaust gas purifying apparatus 2 immediately raises the temperature of the exhaust gas purifying apparatus 2 to a predetermined temperature (about 400 degrees) when the internal combustion engine is in a low temperature state such as immediately after starting, so that the exhaust gas purifying efficiency is improved. Need to raise. Therefore, considering that the exhaust gas temperature becomes higher as it approaches the internal combustion engine,
In order for hot exhaust gas to flow into the exhaust gas purification device 2,
The exhaust gas purification device 2 is arranged close to the internal combustion engine (Fig. 2).

Next, the mass damper 1 for reducing the radiated sound.
4 will be described in detail. As shown in FIG.
The mass damper 14 of this embodiment includes a mass (mass body) 25 and a mounting bracket 26. Mounting bracket 26
Is formed into a U-shape by pressing a rectangular SUS plate. Further, at both ends of the mounting bracket 26, mounting flanges 17 and 18 that are bent in the U-shaped outward direction are also formed by the pressing process. The mass 25 is fixed to the space 19 side surrounded by the U-shaped portion of the mounting bracket 26 by welding or mechanical coupling such as bolting. Then, the U-shaped opening 20 is closed by the mounting counterpart, and the mounting flanges 17 and 18 of the mounting bracket and the mounting counterpart (independent exhaust passage side wall 21 in this embodiment) are welded. To join.

Here, the mounting bracket 26 is formed in a U-shape, and the space 25 surrounded by the U-shape is provided with a mass 25.
The reason for mounting is to effectively use the space in the engine rule of the vehicle in which a large number of various parts exist, and to prevent interference with other parts. Therefore, FIG.
As shown in (b), even if the mass 25 is mounted on the side opposite to the space 19 side surrounded by the U-shaped portion of the mounting bracket 26, the function as the mass damper 14 is not deteriorated, and Even if the mounting bracket 26 is formed in a shape other than the U-shape, the function as the mass damper 14 is not deteriorated.

The mounting bracket 26 is made of a material having substantially the same linear expansion coefficient as that of the mating object. In the mounting bracket 26 of the present embodiment, S forming the independent exhaust passages 3 to 6 is formed.
US material is used. This is an independent exhaust passage 3-6
Since the hot exhaust gas passes through the passage, a dimensional change occurs due to thermal expansion.
If 6 is made of a material different from that of the independent exhaust passages 3 to 6, a difference in thermal expansion between the independent exhaust passages 3 to 6 and the mounting bracket 26 occurs, and an excessive amount occurs in the fixing portion 31 between the mounting bracket 26 and the independent exhaust passages 3 to 6. This is to prevent the reliability of the exhaust manifold 1 from being deteriorated due to the generation of stress and the resulting strain in the independent exhaust passages 3 to 6.

Further, even if the mounting bracket 26 has a coefficient of linear expansion substantially the same as that of the side wall of the independent exhaust passage, it is not directly exposed to the exhaust gas, so that a temperature difference from the side wall 21 of the independent exhaust passage occurs. Although there is a concern that stress will be generated at the joint between the two, the mounting bracket 26 is attached to the independent exhaust passage side wall 21.
Since its volume is smaller than that of, there is no problem because a large temperature difference does not occur between the two.

Next, regarding the mounting position of the mass damper 14, in the present embodiment, the mass damper is mounted near the inlet of the collecting portion of the independent exhaust passage. The independent exhaust passage 3 is attached because the independent exhaust passage 3 has a longer axial length (passage length from the mounting flange 16 to the independent exhaust passage collecting portion 7) than the other independent exhaust passages 4 to 6. In addition, since the rigidity is low (easy to vibrate) and the axial length is long, the exhaust gas easily collides with the side wall of the independent exhaust passage 3, and the side wall easily vibrates. Further, the mass damper is attached near the collecting portion 7 because the shape near the collecting portion 7 is relatively plate-like and its rigidity is lower than that of other exhaust manifold parts, and therefore the side wall is easily vibrated. Is.

As described above, it is effective to mount the mass damper 14 on a tube having a relatively long axial length among the plurality of independent exhaust passages. Further, the effect can be expected even if it is attached to the independent exhaust passage having the curved portion. Further, the independent exhaust passages may be attached to a portion where they join, or a plate-like portion such as the collecting portion 7 of the independent exhaust passages 3 to 6.

Further, in this embodiment, since both ends of the mounting bracket 26 of the mass damper 14 are welded and joined, the mounting bracket 26 also has a function as a reinforcing material for the side wall of the independent exhaust passage.

In the present embodiment, the independent exhaust passages 3 to 6 are formed integrally with the collecting portion 7 to form the exhaust manifold 1, but the exhaust manifold 1 may be formed by forming these separately. Good. Further, instead of the SUS plate, SUS pipe may be used to configure the exhaust independent pipes 3 to 6, and the material is SU.
It does not need to be limited to S.

There is no particular limitation on the shape of the mass.
It goes without saying that the mass of the mass 25 must be determined from the relationship with the shape of the independent exhaust passage, the thickness of the side wall of the exhaust manifold, and other factors in order to mute the sound in a specific frequency band. Conversely speaking, only by adjusting the mass of the mass 25, it is possible to expect an effect as a countermeasure against radiation noise of various exhaust manifolds. In this embodiment, the total mass of the mass 25 and the mounting bracket 26 is about 90 g.

The number of mass dampers 14 is not limited to one. The exhaust manifold 1 may be provided with a plurality of masses having the same mass or a plurality of masses having different masses.

FIG. 4 is a graph showing the effect of this embodiment. A conventional exhaust manifold is made of a SUS plate having a plate thickness of 2 mm. According to this graph, it can be seen that the sound of 4 kHz is reduced in the present embodiment, though the plate thickness (1.5 mm) is thinner than that of the conventional exhaust manifold.

Regarding the warm-up property of the exhaust gas purification device, the temperature of the exhaust gas purification device 40 seconds after the start of the internal combustion engine was about 350 degrees in the conventional case.
It rose to 0 degrees.

As another embodiment, the mass damper 1 described above is used.
The same effect can be obtained by arranging ribs at the same position as the mass damper 14 instead of No. 4. The length and thickness of this rib,
The loudness is determined by the radiated sound of the frequency to be reduced. Further, if a stronger rib is formed, the vibration itself of the independent exhaust passage side wall 21 can be suppressed and the generation of radiated sound can be suppressed regardless of the frequency.

As another embodiment, instead of the mass damper 14, the same effect can be obtained by welding the pad at the same position as the mass damper by welding. The amount and width of the weld overlay are determined by the radiated sound of the frequency to be reduced. Further, if the thickness is thick and the padding is applied over a wide range, the vibration of the side wall 21 of the independent exhaust passage is suppressed irrespective of the frequency, and the generation of radiated sound can be suppressed.

[0036]

According to the present invention, the mass body is attached to the side wall of the exhaust pipe so that the mass body serves as a weight to reduce the vibration speed of the side wall and reduce the generation of radiated sound. To do. Further, by changing the mass of the mass body, it is possible to selectively reduce the radiated sound in the unpleasant frequency band.

According to the present invention, since it is not necessary to attach the sound insulation plate, the temperature of the exhaust manifold is not excessively increased, so that the reliability of the exhaust manifold can be maintained.

Further, since the plate thickness of the exhaust manifold is not increased, a material having a small heat capacity such as SUS pipe and SUS plate can be used. Therefore, it becomes easy to secure the warm-up performance of the exhaust gas purification device.

According to the invention of claim 5, in addition to the above effects, since the mass damper mounting bracket and the exhaust manifold have substantially the same linear expansion coefficient, even if the exhaust manifold has a dimensional change due to thermal expansion, the mass damper Excessive stress does not occur at the joint with and the reliability of the exhaust manifold can be secured. Further, since the mass body and the bracket are separately molded, the mass manifold can be applied to exhaust manifolds of various shapes by adjusting the mass of the mass body.

[Brief description of drawings]

FIG. 1 is a top view of an exhaust pipe muffling structure of the present embodiment.

FIG. 2 is a front view of the exhaust pipe silencing structure of the present embodiment.

FIG. 3 is a cross-sectional view of the mass damper 14.

FIG. 4 is a graph showing the muffling effect of the present embodiment. 1 ... Exhaust manifold, 2 ... Exhaust gas purification device 3, 4,
5, 6 ... Independent exhaust passage, 7 ... Independent exhaust passage collecting portion, 8 ...
Upper part, 9 ... Lower part, 10 ... Joint part, 12 ... Mounting bolt hole, 14 ... Mass damper, 16 ... Mounting flange, 17,
18 ... Mounting flange, 21 ... Independent exhaust passage side wall, 22
... Curved part, 23 ... Independent exhaust passage inner wall, 25 ... Mass, 26
… Mounting brackets,

Claims (5)

[Claims] 1. An exhaust manifold structure for an internal combustion engine, wherein a mass body is provided on an outer surface of the exhaust manifold. 2. An exhaust manifold structure having a plurality of independent exhaust passages, wherein a mass body is provided on a side wall of the independent exhaust passage having the longest axial length among the independent exhaust passages. 3. An exhaust manifold structure having a plurality of independent exhaust passages, wherein a mass body is provided on a wall forming a gathering portion where the independent exhaust passages are gathered. 4. An exhaust manifold structure having an independent exhaust passage having a curved portion or a bent portion, wherein a mass body is provided on a side wall of the curved portion or the bent portion. 5. The mass body according to any one of claims 1 to 4 is attached to a bracket having a linear expansion coefficient substantially the same as that of the exhaust manifold, and the bracket to which the mass body is attached is fixed to an outer surface of the exhaust manifold. The exhaust manifold structure according to any one of claims 1 to 4, wherein