JPH11280470A - Exhaust manifold shape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lengthen a reaching time of pressure wave and thereby improve torque, by installing a first pipe which connects branch pipes successively coupled up to each cylinder of an internal combustion engine respectively, and connecting a roughly linear second pipe to its downstream part, and installing a catalyst or a reflection part of the pressure wave on a part in the direct downstream of the second pipe. SOLUTION: First to fourth branch pipes 4 (4-1 to 4-4), connected to first to fourth cylinders, #1 to #4, of a 4-cylinder internal combustion engine 2, are connected successively by a first pipe 6, and a roughly linear second pipe 8 is connected to the downstream part of the first pipe 6, and also a catalyst 10, which functions as a reflection part of a pressure wave simultaneously, is arranged on a part in the direct downstream of the second pipe 8. In this case, the second pipe is fixed so as to have a larger passage diameter d2, namely 1.5 d1 or larger, compared with each passage diameter d1 of branch pipes 4. Consequently, the pressure wave is damped to thereby aim to improve the output torque of an engine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust manifold, and more particularly to an exhaust manifold having a longer propagation distance of pressure waves, a longer arrival time of pressure waves reflected from a catalyst or a reflection portion of the pressure waves, and a pressure wave of exhaust gas. The delay and the amplitude become small, so that fresh air can be sucked in from the beginning of the intake, the torque of the internal combustion engine can be improved, and the pressure wave of the exhaust gas is attenuated to improve the performance in a wide range of the internal combustion engine. The present invention relates to an exhaust manifold shape which can be made compact and lightweight.

[0002]

2. Description of the Related Art An internal combustion engine having a plurality of cylinders mounted on a vehicle is provided with an exhaust passage for discharging exhaust gas from each cylinder and a catalyst for purifying exhaust harmful components in the exhaust passage. is there.

One such exhaust manifold configuration is disclosed in Japanese Patent Application Laid-Open No. 9-53446. An exhaust device for an internal combustion engine disclosed in this publication is characterized in that a plurality of exhaust ports of a cylinder head are provided with an inclined virtual axis whose opening center on one side surface of the cylinder head is vertically inclined with respect to an imaginary axis parallel to the crankshaft axis. The exhaust manifold is formed so as to be positioned on a line, and a branch pipe of an exhaust manifold formed by projecting a short tubular branch pipe from a straight tubular main pipe part provided with a coupling flange at one end opening is connected to the opening of each exhaust port. The manufacturing cost of the manifold is reduced, and performance degradation due to increased intake resistance is avoided.

[0004]

Meanwhile, in the conventional exhaust manifold shape, there is a layout in which exhaust interference occurs as shown in FIG.

That is, as shown in FIG.
2, four first to fourth cylinders # 1, # 2, # not shown
3, # 4, and these first to fourth cylinders # 1, # 2,
In # 3 and # 4, the first to fourth branch pipes 104-1 and 104-
2, 104-3 and 104-4 are provided in contact with each other. These first to fourth branch pipes 104-1, 104-2, 10
4-3 and 104-4 are formed substantially in parallel.

An upstream portion of the first pipe portion 106 is provided so as to be substantially orthogonal to the downstream end portion of the first branch pipe 104-1. At this time, the first branch pipe 104-1 and the first pipe section 106 can be formed integrally.

[0007] As it moves to the downstream side of the first pipe section 106, the second and third branch pipes 104-2, 104-3 are provided.
Are connected so as to be substantially orthogonal to each other.

Further, at a connection portion between the fourth branch pipe 104-4 and the first pipe section 106, the connection section is provided with a second pipe section 108 substantially linearly with respect to the fourth branch pipe 104-4.
Is connected, and a catalyst 110 is disposed downstream of the second pipe section 108.

As a result, the reflection point of the pressure wave of the exhaust gas becomes a connection portion between the fourth branch pipe 104-4 and the first pipe portion 106, and the propagation distance of the pressure wave is determined by each of the cylinders # 1, # 2,
# 3, # 4, the fourth branch pipe 104-4, and the first pipe section 10
This is a distance that includes the pressure wave reflection point at the connection portion with the pressure wave 6, and the propagation distance is short. As shown in FIG. 17, there is a disadvantage that exhaust interference is caused.

As a layout for reducing the above-described exhaust interference, for example, the following three measures can be considered. (1) The so-called "octopus foot exhaust" shape in which the independent portion of the exhaust pipe of each cylinder is lengthened. (2) In an internal combustion engine in which the ignition sequence is, for example, # 1, # 3, # 4, and # 2, first, in the exhaust pipe collecting policy, #
1 and # 4, and # 2 and # 3, respectively.
A shape in which one is assembled and the length to the final assembly point is secured. (3) A shape having exhaust interference as shown in FIGS.

Here, the shapes having the exhaust interference shown in FIGS. 18 and 19 will be described. First to fourth independent exhaust pipes 204-1 having first to fourth independent exhaust passages (not shown) in the internal combustion engine 202, respectively. 204-2, 204-3, 204
-4 are connected to each other, and the first to fourth independent exhaust pipes 204-1, 204-2, 204-3, 204
-4 is connected to a first passage extension 292 forming a first volume.

The first to fourth independent exhaust passages are formed to have a predetermined length L1 to L4, respectively, and have a predetermined passage cross-sectional area.

A pipe portion 294 having a passage sectional area larger than the passage sectional area of the first to fourth independent exhaust passages and having a length L5 is connected to a downstream portion of the first passage expansion portion 292. Then, a catalyst 210 is provided downstream of the pipe 294 in communication therewith.

At this time, the pressure wave of the exhaust gas is reflected at the open end at the first passage expansion portion 292 and is reflected at the immediately upstream portion of the catalyst 210 at the closed end.

However, in the first and second measures for reducing the exhaust interference described above, a large space around the internal combustion engine is required, so that the layout is difficult, and the weight and cost increase. There is a disadvantage of being connected.

In the first measure and the second measure, the catalyst is arranged downstream of the collecting point, so that the temperature of the exhaust gas is reduced by the longer distance from the internal combustion engine to the catalyst. In addition, there is a disadvantage that the warm-up of the catalyst is delayed, which is disadvantageous for purifying the exhaust gas.

Further, in the third measure, the reflection point of the pressure wave of the exhaust gas is divided into two, so that the wave propagation distance can be made relatively long, and attenuation of the pressure wave and exhaust interference can be eliminated. However, since the reflection point is divided into two, in the open-end reflection in which the wave propagation distance is shortened, the exhaust interference cannot be effectively eliminated, and an improvement has been desired.

[0018]

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned disadvantages, the present invention relates to an exhaust manifold which is connected to each cylinder of an internal combustion engine and connected to a catalyst at a downstream end. A branch pipe connected to each cylinder of the internal combustion engine, a first pipe portion connecting the branch pipes sequentially is provided, and a first pipe portion connected substantially linearly downstream of the first pipe portion is provided. Two pipe sections are provided, and the catalyst or the reflection section of the pressure wave is connected and provided directly downstream of the second pipe section.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION
The propagation distance of the pressure wave is increased, the arrival time of the pressure wave reflected from the catalyst or the reflection portion of the pressure wave is increased, the pressure wave of the large exhaust gas to the intake / exhaust overlap in the cylinder is delayed and the amplitude is reduced, and the intake Fresh air is sucked in from the beginning to improve the torque of the internal combustion engine, attenuate the pressure wave of the exhaust gas, improve the performance in a wide range of the internal combustion engine, and reduce the size and weight.

[0020]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention;

FIG. 1 to FIG. 9 show a first embodiment of the present invention. In FIG. 1, reference numeral 2 denotes an internal combustion engine having multiple cylinders mounted on a vehicle, for example, four cylinders.

This internal combustion engine 2 has first to fourth cylinders # 1,
# 2, # 3, and # 4. And these first
The first to fourth branch pipes 4-1, 4-2, 4-3, and 4-4 are provided in communication with the fourth to fourth cylinders # 1, # 2, # 3, and # 4, respectively.

The first to fourth branch pipes 4-1 and 4-1.
First pipe section 6 for sequentially connecting 4-2, 4-3, and 4-4
And a second pipe portion 8 connected substantially linearly downstream of the first pipe portion 6, and a catalyst 10 connected and provided immediately downstream of the second pipe portion 8. I do.

More specifically, as shown in FIG. 1, the first pipe section 6 includes first to fourth branch pipes 4-1, 4-2, 4-3, 4-3.
-4 is formed to have substantially the same passage diameter as the passage diameter. In the first embodiment, the first branch pipe 4-1 and the first pipe section 6 will be described with reference numerals as separate bodies, but the first branch pipe 4-1 and the first pipe section will be described. 6 can be formed integrally.

Although the catalyst 10 is connected to a portion immediately downstream of the second pipe portion 8, if there is a portion which functions as a pressure wave reflection portion at a portion upstream of the catalyst 10,
The catalyst 10 is located at a position separated from the portion immediately downstream of the second pipe portion 8.
It is also possible to provide.

Further, when connecting the second pipe section 8 to the downstream side of the first pipe section 6, the second pipe section 8 is connected substantially linearly, and the flow of exhaust gas is directed straight to the catalyst 10.

Then, as shown in FIG. 1, for example, the second pipe section 8 is connected to first to fourth branch pipes 4-1, 4-2, 4-3,
The passage diameter d2 is set to be larger than the passage diameter d1 of 4-4. At this time, when the magnitude relationship between the passage diameters is represented by numerical values, the first to fourth branch pipes 4-1, 4-2, 4-3, 4-4
For each passage diameter d1, the passage diameter d2 of the second pipe portion 8
Is set to 1.5 times or more.

The length KL1 of the first pipe section 6 is determined by the center line C1 of the first branch pipe 4-1 and the center line C4 of the fourth branch pipe 4-4.
And the second pipe portion 8
Can be represented by the distance from the center line C4 of the fourth branch pipe 4-4 to the catalyst 10, and the length KL2 of the second pipe section 8 is about 100 mm.

The first to fourth cylinders # 1 and # 1 of the internal combustion engine 2
The first to fourth branch pipes 4- which respectively communicate with # 2, # 3, and # 4
In 1, 4-2, 4-3, and 4-4, while maintaining the substantially linear connection between the first pipe 6 and the second pipe 8, the second to second pipes are maintained.
Fourth branch pipes 4-2, 4-3, and 4-4 are provided so as to be connected to the first pipe section 6 so as to be substantially orthogonal.

That is, on the left side of FIG. 1, the first branch pipe 4-1 and the left end of the first pipe section 6 are connected at a point P1,
At a point P1, which is a point shifted from the point P1 to the right side in FIG. 1, the second branch pipe 4-2 is connected substantially orthogonally to the first pipe portion 6, and the point P2 is shifted to the right side in FIG. At a point P3, the third branch pipe 4 is substantially orthogonal to the first pipe section 6.
-3 is connected.

Then, at a point shifted from the point P2 to the right side in FIG. 1, that is, at a point P3 which is a connection site between the first pipe part 6 and the second pipe part 8, the first pipe part 6 and the second pipe part The fourth branch pipe 4-4 is connected substantially orthogonally to the pipe 8.

Next, the operation of this embodiment will be described.

The first to fourth cylinders # 1 and # 1 of the internal combustion engine 2
The exhaust gas generated in # 2, # 3, and # 4 is the first to fourth
The fluid flows into the branch pipes 4-1, 4-2, 4-3, and 4-4, respectively.

The exhaust gas flowing into the first branch pipe 4-1 passes through the point P1 and then reaches the catalyst 10 through the first pipe section 6 and the second pipe section 8. At this time, the first pipe section 6 and the second pipe section 8 are connected in a substantially straight line, and the exhaust gas is directed straight to the catalyst 10.

While the flow of the exhaust gas flowing into the first branch pipe 4-1 is the main flow, the connection shape from the second branch pipe 4-2 and the third and fourth branch pipes 4-3 and 4-4 is the main flow. Do not disturb.

When the above-mentioned exhaust gas passes through the second pipe section 8, the pressure wave of the exhaust gas is attenuated by making the second pipe section 8 larger in diameter than the first pipe section 6. At the same time, the irregular reflection in the second tube section 8 is also attenuated.

At this time, the propagation distance of the pressure wave becomes large from the internal combustion engine 2 to the catalyst 10 including the first and second pipe portions 6 and 8, and, for example, in the case of the third branch pipe 4-3, the start of the exhaust is started. From the internal combustion engine 2 through point P3,
Since it passes through the first and second pipe portions 6 and 8 and reaches the catalyst 10, it takes a long time before the pressure wave reflected from the catalyst 10 reaches the first branch pipe 4-1. It will be.

Thus, the second pipe section 8 is connected and provided substantially linearly downstream of the first pipe section 6, and the catalyst 10 is connected and provided immediately downstream of the second pipe section 8. As a result, the propagation distance of the pressure wave can be increased. For example, in the case of the third branch pipe 4-3, the point P3
After passing through the first and second pipe portions 6 and 8 and reaching the catalyst 10, the pressure wave reflected from the catalyst 10 becomes large before reaching the first branch pipe 4-1. It takes time, and the large pressure wave of the exhaust gas to the intake / exhaust overlap in the cylinder # 1 is delayed and the amplitude is small as shown in FIG. 4, so that fresh air can be taken in from the beginning of intake. Thus, the torque of the internal combustion engine can be improved.

Further, the passage diameter d2 of the second pipe portion 8 is set to be 1: 1 with respect to each passage diameter d1 of the first to fourth branch pipes 4-1, 4-2, 4-3 and 4-4. By setting it to be five times or more, the pressure wave of the exhaust gas is attenuated in the second pipe part 8 and the irregular reflection in the second pipe part 8 is also attenuated. In this case, the performance can be improved, which is practically advantageous.

Further, by connecting and providing the second pipe portion 8 substantially linearly downstream of the first pipe portion 6, the internal combustion engine 2 is provided.
The layout can be made more compact and lighter, and the main flow of exhaust gas is directed straight to the catalyst 10, which can contribute to an improvement in the warm-up performance of the catalyst 10 described later.

Further, since the catalyst 10 is connected and provided immediately downstream of the second pipe portion 8, the catalyst 10 can be disposed close to the engine without impairing the engine performance.
The warm-up performance of the catalyst 10 can be improved, which is practically advantageous.

FIG. 10 shows a second embodiment of the present invention. In the second embodiment, portions that perform the same functions as those in the first embodiment will be described with the same reference numerals.

The feature of the second embodiment is that the first to fourth branch pipes 4 to 4 are similar to the first embodiment.
1, 4-2, 4-3, 4-4 and the first pipe 6 are formed, and the passage diameter of the second pipe 12 connected to the first pipe 6 in a substantially linear manner is set to the first pipe diameter. The point is that the diameter is substantially the same as the diameter of the passage of the pipe portion 6.

That is, as shown in FIG.
Of the first to fourth cylinders # 1, # 2, # 3, and # 4
The branch pipes 4-1, 4-2, 4-3 and 4-4 are communicated with each other, and the first to fourth branch pipes 4-1 and 4-4 are connected.
2, 4-3 and 4-4 are disposed so as to be substantially orthogonal to the first pipe portion 6.

The diameter of the passage of the second pipe 12 is the same as that of the first pipe 6 or the first to fourth branch pipes 4-1, 4-2, 4-3,
The catalyst 10 is formed so as to be substantially the same as the passage diameter of 4-4, and is connected to a portion immediately downstream of the second pipe portion 12.

In this case, the propagation distance of the pressure wave can be made longer than that of the conventional one, and the arrival time of the pressure wave reflected from the catalyst 10 becomes longer. Furthermore, the pressure wave of the large exhaust gas to the intake / exhaust overlap in the cylinder # 1 is delayed and the amplitude becomes small, so that it is possible to take in fresh air from the beginning of intake and to improve the torque of the internal combustion engine. Can be.

Further, the pressure wave of the exhaust gas is slightly attenuated in the second pipe portion 12, and the irregular reflection in the second pipe portion 12 is also slightly attenuated.
It is possible to improve the performance in a wide range, which is practically advantageous as in the case of the first embodiment.

Further, by connecting and providing the second pipe portion 12 in a substantially straight line downstream of the first pipe portion 6, the first pipe portion 12 is provided.
As in the case of the embodiment, the internal combustion engine 2 can be made compact in layout, can be reduced in weight, and the main flow of exhaust gas is directed straight to the catalyst 10, so that the warm-up of the catalyst 10 described later It can contribute to the improvement of performance.

Further, since the catalyst 10 is connected and provided immediately downstream of the second pipe section 12, the catalyst 10 can be connected without impairing the engine performance, similarly to the first embodiment. The catalyst 10 can be arranged in the vicinity, and can contribute to improvement of the warm-up performance of the catalyst 10, which is practically advantageous.

FIGS. 11 and 12 show a third embodiment of the present invention.

The feature of the third embodiment is that the passage diameter of the second pipe portion 22 is formed so as to gradually increase toward the downstream side.

That is, as shown in FIGS. 11 and 12, the second pipe portion 22 is formed in a divergent shape gradually increasing toward the downstream side.

The direction in which the diameter of the passage of the second pipe portion 22 widens is, as apparent from FIG. 11, a direction away from the internal combustion engine (not shown), and, as apparent from FIG. 12, a direction away from the internal combustion engine (not shown). It has become.

At this time, when the second pipe section 22 is connected to the first pipe section 6 as shown in FIG. 12, the second pipe section 22 is connected so as to be directed obliquely downward. If the second pipe portions 6 and 22 are not substantially distorted in a so-called straight pipe shape that is connected to the second pipe portions 6 and 22 substantially linearly, they do not function as a pressure wave reflection portion and have no problem.

In this case, the propagation distance of the pressure wave can be made longer than that of the prior art, and the arrival time of the pressure wave reflected from the catalyst (not shown) becomes longer. Similarly, the pressure wave of the large exhaust gas to the intake / exhaust overlap in the cylinder # 1 is delayed and the amplitude becomes small, so that the fresh air can be taken in from the beginning of the intake, and the torque of the internal combustion engine is increased. Improvement can be achieved.

Further, by increasing the passage diameter of the second pipe portion 22 gradually toward the downstream side, the pressure wave of the exhaust gas is attenuated in the second pipe portion 22 and the second pipe portion 2 is reduced.
As a result, the performance can be improved in a wide range of the internal combustion engine, which is practically advantageous as in the first and second embodiments.

Further, by connecting and providing the second pipe portion 22 downstream of the first pipe portion 6 without greatly distorting the straight pipe shape, the same as in the first and second embodiments described above. In addition, the layout of the internal combustion engine can be reduced in size and weight, and the main flow of exhaust gas can be directed to the catalyst, which can contribute to the improvement of the warm-up performance of the catalyst described later.

Further, since the catalyst is connected to the portion immediately downstream of the second pipe portion 22, the catalyst can be brought into close proximity without impairing the engine performance as in the first and second embodiments. It can be arranged and can contribute to improvement of the warm-up performance of the catalyst, which is practically advantageous.

The present invention is not limited to the above-described first to third embodiments, and various application modifications are possible.

For example, in the first and third embodiments of the present invention, only the passage diameter of the second pipe portion is increased, but as shown in FIG. 13, the first and second pipe portions 32, 34 are provided.
Is formed so that the diameter of the passage gradually increases toward the downstream side,
A configuration (SG1) in which the pressure wave of the exhaust gas is attenuated in the first and second pipe portions 32 and 34 and the irregular reflection in the second pipe portion 34 is also attenuated. At this time, the direction in which the diameters of the passages of the first and second pipe portions 32 and 34 expand is set in a direction away from the internal combustion engine 2 as shown in FIG.

The direction in which the passage diameters of the first and second pipe portions expand may be a shape (SG2) that gradually increases in at least one of the horizontal direction and the vertical direction. That is, as shown in FIG. 14, when the pipe portion 42 including the first and second pipe portions is provided, the shape can be gradually increased in the horizontal direction as shown by the one-dot chain line in FIG. 14. As shown by a two-dot chain line in FIG. 14, the shape can be gradually increased in the vertical direction. And at this time,
It is not necessary to extend both left and right or back and forth in the horizontal direction, or both up and down in the up and down direction, and it is also possible to extend to either one depending on the layout of the internal combustion engine or other factors.

Further, as shown in FIG. 15, first to fourth branch pipes 4-1 to 4-2, 4-3 and 4-4 are provided in communication with the internal combustion engine 2 and the first to fourth branch pipes 4-1 to 4-2 are connected. 4-branch pipe 4-
1, 4-2, 4-3, and 4-4 are disposed so that the first pipe section 52 and the second pipe section 54 are substantially orthogonal to each other, and the catalyst 10 is connected to a portion immediately downstream of the second pipe section 56. In the configuration described above, the second branch pipe 4
When moving from -2 to the fourth branch pipe 4-4, the passage diameter of the first and second pipe parts 52, 54 can be formed so as to increase stepwise toward the downstream side (SG3). .

That is, as shown in FIG. 15, when the passage diameter of the first to fourth branch pipes 4-1, 4-2, 4-3, 4-4 is D, the first branch pipe 4-1 The passage diameter of the first pipe portion 52 between the second branch pipe 4-2 and the second branch pipe 4-2 is set to be substantially the same D, and the first pipe between the second branch pipe 4-2 and the third branch pipe 4-3 is formed. The passage diameter of the portion 52 is set to D1 larger than D,
First pipe portion 52 between branch pipe 4-3 and fourth branch pipe 4-4
The passage diameter of the portion is set to D2 which is larger than D1. Then, the diameter of the passage of the second space 54 is equal to or equal to D2.
D3, which is larger than D3. At this time, the spreading direction of the passage diameter can be arbitrarily set.

In this case, the first and second pipe portions 52 and 54 having the passage diameter gradually increasing toward the downstream side can effectively attenuate the pressure wave of the exhaust gas, and Even diffuse reflection can be effectively attenuated, and performance can be improved in a wide range of the internal combustion engine.

[0065]

As apparent from the above detailed description, according to the present invention, each cylinder of the internal combustion engine is communicated,
In the exhaust manifold shape provided with a catalyst connected to the downstream end, a branch pipe is provided to communicate with each cylinder of the internal combustion engine, and a first pipe section for connecting these branch pipes in sequence is provided. A second pipe portion connected in a substantially straight line is provided downstream of the pipe portion, and a catalyst or pressure wave reflection portion is connected and provided immediately downstream of the second pipe portion. The distance can be large, the arrival time of the pressure wave reflected from the catalyst or the reflection part of the pressure wave is large, the pressure wave of the large exhaust gas to the intake and exhaust overlap in the cylinder is delayed and the amplitude is small, Fresh air can be taken in from the beginning of the intake, and the torque of the internal combustion engine can be improved. Further, the pressure wave of the exhaust gas is attenuated in the second pipe portion, and is also attenuated by irregular reflection in the second pipe portion, so that the performance can be improved in a wide range of the internal combustion engine. It is advantageous. Further, by connecting and providing the second pipe portion in a substantially straight line downstream of the first pipe portion, the internal combustion engine can be made compact in layout, can be reduced in weight, and the main flow of exhaust gas can be reduced. Will be directed to the catalyst or the reflection part of the pressure wave. In the case of a catalyst, the catalyst can be arranged close to the catalyst without impairing the engine performance, and the warm-up performance of the catalyst can be improved, which is practically advantageous. It is.

[Brief description of the drawings]

FIG. 1 is a schematic view of an exhaust manifold of an internal combustion engine showing a first embodiment of the present invention.

FIG. 2 is an enlarged view of a portion viewed from an arrow in FIG. 1;

FIG. 3 is a diagram illustrating a relationship between an engine speed and a shaft torque.

FIG. 4 is a diagram showing a relationship between a crank angle and intake pressure and exhaust pressure.

FIG. 5 is a front view of a catalyst.

FIG. 6 is a cross-sectional view taken along line V〓-V〓 of FIG. 5;

FIG. 7 is a cross-sectional view taken along line V〓〓-V〓〓 of FIG. 5;

FIG. 8 is a left side view of the catalyst.

FIG. 9 is a right side view of the catalyst.

FIG. 10 is a schematic view of an exhaust manifold of an internal combustion engine showing a second embodiment of the present invention.

FIG. 11 is an enlarged plan view of an exhaust manifold showing a third embodiment of the present invention.

FIG. 12 is an enlarged front view of the exhaust manifold.

FIG. 13 is a schematic view of an exhaust manifold of an internal combustion engine showing another first embodiment of the present invention.

FIG. 14 is a schematic enlarged view of a tube showing another second embodiment of the present invention.

FIG. 15 is a schematic view of an exhaust manifold of an internal combustion engine showing another third embodiment of the present invention.

FIG. 16 is a schematic view of an exhaust manifold of an internal combustion engine showing the first prior art of the present invention.

FIG. 17 is a diagram showing a relationship between a crank angle and intake pressure and exhaust pressure.

FIG. 18 is a schematic view of an exhaust manifold of an internal combustion engine showing a second prior art of the present invention.

FIG. 19 is an enlarged view of a main part of an exhaust manifold of the internal combustion engine.

[Explanation of symbols]

 2 Internal combustion engine # 1 First cylinder # 2 Second cylinder # 3 Third cylinder # 4 Fourth cylinder 4-1 First branch pipe 4-2 Second branch pipe 4-3 Third branch pipe 4-4 Fourth branch Tube 6 First tube 8 Second tube 10 Catalyst

Claims (6)

[Claims] 1. Communicating with each cylinder of an internal combustion engine,
In an exhaust manifold shape provided with a catalyst connected to the downstream end, a branch pipe is provided to communicate with each cylinder of the internal combustion engine, and a first pipe section for connecting these branch pipes in sequence is provided. A second pipe portion connected in a substantially straight line is provided downstream of the first pipe portion, and the catalyst or pressure wave reflection portion is connected and provided at a portion immediately downstream of the second pipe portion. And exhaust manifold shape. 2. The exhaust manifold shape according to claim 1, wherein the exhaust manifold shape is such that a passage diameter of the second pipe portion is set to be larger than a passage diameter of each branch pipe. 3. The exhaust manifold has a first to fourth branch pipes respectively connected to four first to fourth cylinders of the internal combustion engine, and a first pipe section and a second pipe section. The exhaust manifold shape according to claim 1, wherein the second to fourth branch pipes are connected to be substantially orthogonal to the first pipe portion while maintaining a substantially linear connection state. 4. The exhaust manifold shape according to claim 1, wherein the exhaust manifold shape is formed so that a passage diameter of the first and second pipe portions gradually increases toward the downstream side. 5. The exhaust manifold has a shape in which at least one of a horizontal direction and a vertical direction is used when the passage diameters of the first and second pipe portions are gradually increased toward the downstream side. The exhaust manifold shape according to claim 4, wherein the exhaust manifold shape is gradually increased. 6. The exhaust manifold shape is formed so as to gradually increase the passage diameters of the first and second pipe portions toward the downstream side when transitioning from the second branch pipe to the fourth branch pipe. The exhaust manifold shape according to claim 1.