JP2000054848A - Exhaust pressure control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To most suitably control the intake and exhaust to improve the combustion efficiency by providing an exhaust junction part for joining secondary exhaust gas to the high-speed primary exhaust gas discharged from a primary exhaust port from the circumferential direction, and a final exhaust rectifying part for discharging these exhaust gases to the outside at a proper flow velocity. SOLUTION: An expansion chamber 2 is extended on the downstream side of an exhaust gas inlet part 1 connected to the exhaust pipe of an internal combustion engine, and a primary exhaust port 3 is opened to the center part of the downstream end. The secondary exhaust system inlet 4 of a secondary exhaust passage 5 is opened to the upstream edge of the throttle wall surface 31 of the primary exhaust port 3 with a fixed angle space, and a secondary exhaust system outlet 6 is opened to the vicinity of the downstream end outside of the primary exhaust port 3 on the downstream end of the secondary exhaust system passage 6 with a fixed angle space. A primary exhaust and secondary exhaust junction part 7 for joining the exhaust gas passed through the primary exhaust port 3 with the secondary exhaust gas passed through the secondary exhaust system outlet 6 is arranged on the downstream side in the outlet end of the primary exhaust port 3. Further a final rectifying exhaust port 8 for finally releasing the exhaust gas to the atmosphere is arranged on the downstream side of the junction part 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust pressure control apparatus for controlling an exhaust gas emission state in an internal combustion engine to improve operation efficiency and reduce unnecessary substances in the exhaust gas. is there.

[0002]

2. Description of the Related Art An internal combustion engine which is widely used at present takes fuel and oxygen into a cylinder during an intake stroke, compresses the intake air to a predetermined pressure in a compression stroke, and applies the compressed intake air to a gasoline engine. Ignition by electric sparks, and self-ignition by high temperature in diesel engines, causing the fuel to burn instantaneously in the explosion stroke, extracting the energy at that time as mechanical power, and discharging the combustion exhaust gas in the exhaust stroke. . Therefore, in order to improve the efficiency of the internal combustion engine, it is necessary to execute the states of fuel intake, compression, explosion, and exhaust under optimal conditions.

[0003] In order to optimize the combustion state of such fuel, various improvements have been made in terms of the structure of the engine combustion section, the control method, and the like, and there are many specific examples. For example, there are those that control the supply of fuel by incorporating a microcomputer, and those that go a step further by eliminating gasifiers (carburetors) and fuel vaporizers that were conventionally provided outside cylinders, and gasoline engines that directly inject into cylinders It has been developed and has been effective in improving efficiency. Efforts to improve the efficiency of diesel engines using heavy oil or light oil as fuels have been made by improving the fuel injection system and the shape of the combustion chamber.

It is natural that the intake of fuel and air, and thus the intake, is important for improving the efficiency of an internal combustion engine, but equally important is the treatment of exhaust gas. No matter how the combustion efficiency is improved, it cannot be 100% because exhaust gas contains considerable unburned substances, and carbon oxides (COx) and nitrogen oxides (NOx) And various kinds of unnecessary substances such as sulfur oxides (SOx), which are said to be causes of air pollution, photochemical smog, and global warming.

[0005] The unburned substances in the exhaust gas are the energy held by the fuel, and are reduced as the combustion approaches the complete combustion. However, since the state has not reached the ideal state, considerable energy is released into the atmosphere. Will be. Ordinary exhaust gas is also high in temperature and pressure and has a considerable flow velocity. Naturally, such unburned substances are naturally a part of the energy held by the fuel, but the high temperature, high pressure, flow velocity, sound, etc. of the exhaust gas have each changed the energy of the fuel. Things. Therefore, by reducing the amount of waste by utilizing each of these energy sources, including the effective use of unburned components,
This will provide good results for the global environment and also improve the thermal efficiency of the internal combustion engine.

[0006]

SUMMARY OF THE INVENTION The present invention focuses on such circumstances, and optimally controls the state of exhaust gas exhaustion in an internal combustion engine, thereby optimally controlling intake and exhaust, and through this, combustion. It is an object of the present invention to provide an exhaust pressure control device that can improve efficiency and can also exert an effect on prevention of air pollution and global warming.

[0007]

According to the present invention, there is provided an exhaust gas introduction portion connected to an exhaust system of an internal combustion engine, and at least a downstream side of a gas flow of the exhaust gas introduction portion and having an inner diameter directed toward the downstream side. An exhaust gas expansion chamber surrounded by a diffusion wall configured to gradually expand and a throttle wall whose inner diameter is gradually reduced so as to taper further downstream toward the downstream side; A primary exhaust port opened at the tapered central portion of the throttle wall on the downstream side, and a secondary exhaust system flow path formed outside the primary exhaust port opened at the center of the throttle wall, A secondary exhaust system flow path that opens to the exhaust gas expansion chamber at the upstream edge and allows the exhaust gas to flow while gradually moving the exhaust gas toward the center on the downstream side; and an exhaust gas passage that passes through the primary exhaust port. Secondary exhaust that has passed through the secondary exhaust system flow path A primary exhaust / secondary exhaust junction where the gas and the secondary exhaust gas are merged again via a secondary exhaust system outlet, wherein the secondary exhaust gas merges with the high-speed primary exhaust gas discharged from the primary exhaust port from the outer peripheral direction thereof This is an exhaust pressure control device including a primary exhaust / secondary exhaust merging section that joins while sucking air, and a final exhaust rectifying section that discharges these exhaust gases to the outside at an appropriate flow rate.

[0008] The capacity of the exhaust gas expansion chamber, the diffusion angle of the diffusion wall constituting the exhaust gas expansion chamber, the throttle angle of the primary exhaust port, the throttle wall connected to the secondary exhaust system flow path, and the secondary exhaust gas from the exhaust gas expansion chamber. The number, size, mounting position, and the like of the communication ports connected to the system flow path should be appropriately changed depending on the type and capacity of the internal combustion engine to be applied, the use and operation mode of the internal combustion engine, and the like.

For example, if the capacity of the exhaust gas expansion chamber is to be set so that the characteristics of the internal combustion engine to which it is applied are suitable for high-speed operation, it should be reduced, and the capacity of the exhaust gas expansion chamber should be set so as to be suitable for low-speed operation. If you try, it should be bigger. That is, when the capacity of the exhaust gas expansion chamber is reduced, the pressure rise (back pressure generation) due to the introduction of the exhaust gas is accelerated, and the subsequent discharge of the exhaust gas through the primary exhaust port and the secondary exhaust system flow path is reduced. This is because the operation is performed at a high speed, and when the capacity of the exhaust gas expansion chamber is increased, the opposite occurs. The specific capacity should be determined experimentally for each internal combustion engine to be applied based on the above assumptions.

According to the exhaust pressure control device of the present invention, when the exhaust gas discharged from the exhaust valve of the internal combustion engine is introduced,
The exhaust gas initially travels through an exhaust gas inlet having an internal diameter equivalent to the extension of the exhaust pipe of the internal combustion engine. In this case, the flow of the exhaust gas in the exhaust stroke of the internal combustion engine is discharged from the opened exhaust valve in a short time, so that the flow becomes a pulsed traveling wave, the highest speed is at the center of the pipe, and the flow of the exhaust gas is generated at the pipe wall. A steep warhead-like traveling wave that becomes slower as it gets closer is formed.

The exhaust gas which travels as a warhead-like traveling wave enters the exhaust gas expansion chamber, and its pipe wall is inclined so that it becomes a diffusion wall and diffuses divergently. In the direction of expansion, expanding and diffusing,
When the pressure is reduced, the velocity difference between the portion close to the tube wall and the central portion is reduced, and therefore, the wave front inclination of the warhead-like traveling wave is reduced. Therefore, at this time, the exhaust gas discharged from the cylinder flows into the exhaust gas expansion chamber at an extremely high speed.

The exhaust gas whose warhead-like traveling wave has a gentle wave front inclination as described above travels to the latter half of the exhaust gas expansion chamber, and collides with a throttle wall narrowed down by a throttle angle that gradually reduces the inner diameter. Then, it proceeds while receiving resistance toward the primary exhaust port at the central portion on the most downstream side. When the exhaust gas collides with the throttle wall in this way, the pressure is increased again, and this pressure rise becomes an instantaneous back pressure that is pushed back to the exhaust system upstream side.

Thus, such pressure changes in the exhaust system control the superposition time during the transition from the exhaust stroke to the intake stroke of the internal combustion engine. As described above, when the exhaust gas first proceeds to the exhaust gas expansion chamber, the pressure decreases as the volume of the exhaust gas increases. Therefore, the exhaust gas in the cylinder is
Until the pressure in the exhaust gas expansion chamber increases, the exhaust gas is discharged at an extremely high speed toward the exhaust gas expansion chamber. Therefore, in the first half of the superimposition time when both the exhaust valve and the intake valve are open, the internal pressure of the cylinder of the internal combustion engine is reduced by high-speed exhaust, thereby allowing efficient intake to be performed during this time. Is what you get.
Further, thereafter, as described above, the exhaust gas proceeds to the latter half of the exhaust gas expansion chamber and collides with the throttle wall surface, and the pressure is increased again, and this pressure increase is pushed back to the exhaust system upstream side. In the latter half of the superimposition time, this acts to suppress the exhaust of the inhaled raw gas through the exhaust valve.

Part of the exhaust gas that has entered the exhaust gas expansion chamber will eventually travel to the latter half thereof and, as described above, will be throttled by the throttle wall and will have a high pressure and will enter the primary exhaust port. The pressure is increased by the high pressure to exhaust the gas. As described above, the high pressure, which is also the back pressure, further increases the difference from the atmospheric pressure, and thus has the effect of further increasing the discharge speed from the primary exhaust port.

On the other hand, at the outer edge, which is the upstream edge of the throttle wall, outside the primary exhaust port, a communication port to a secondary exhaust system flow path surrounding the primary exhaust port is required at regular angular intervals. Another part of the exhaust gas, which is opened several times and is pressurized by resistance such that it expands and contracts once, flows out to the secondary exhaust system channel through these communication ports.

The two exhaust gases discharged through each of the primary exhaust port and the secondary exhaust system flow path are the primary exhaust gas and the primary exhaust port where the discharge port of the primary exhaust port communicates with the outlet of the secondary exhaust system flow path.
They will be joined at the secondary exhaust junction.

Each exhaust gas flowing through the primary exhaust port and the secondary exhaust system flow path is exhausted by a differential pressure from the atmospheric pressure. In this case, as described above, the exhaust gas flows through the central primary exhaust port. Exhaust gas is accelerated with the pressure rise of the exhaust gas expansion chamber and becomes extremely high speed, and the exhaust gas discharged through the secondary exhaust system flow path further increases the flow speed due to the Venturi effect due to its flow speed, It will be exhausted. The exhaust gas whose pressure has been increased in the exhaust gas expansion chamber in this way is immediately discharged thereafter, and the inside of the exhaust pressure control device including the exhaust gas expansion chamber is depressurized at high speed.

At the final rectification exhaust port, the exhaust gases that have exited from the primary exhaust port and the respective outlets of the secondary exhaust system flow path are merged and discharged to the outside (atmosphere).

The exhaust pressure control device of the present invention has the above-described configuration and functions. As described above, the dimensions, angles, capacities, and the like of each part of the device can be experimentally determined in accordance with the internal combustion engine to be applied, thereby controlling the exhaust pressure, the timing of the pressure change, and the like. . By arbitrarily controlling the exhaust pressure, the pressure in the cylinder during the superimposed time when the intake valve and the exhaust valve are simultaneously opened is appropriately controlled, and the exhaust is efficiently performed, and the intake is also efficiently performed, In addition, it is possible to suppress unnecessary discharge of inhaled raw gas by the back pressure, and after closing the exhaust valve, immediately release the pressure that caused the back pressure, so that it can be used for exhaust in the next cycle. It can prevent any adverse effects. Thus, an appropriate effect is exerted on the inside of the cylinder of the internal combustion engine through the exhaust valve, and the combustion state can be changed efficiently.

According to the exhaust pressure control apparatus of the present invention, the state of intake and exhaust between the operation of the intake valve and the exhaust valve of the target internal combustion engine is improved, and sufficient intake and scavenging are performed smoothly. Therefore, it is possible to obtain high kinetic energy by increasing the combustion efficiency, reduce unburned components in a reflective manner, and reduce various harmful substances in exhaust gas. It is also a thing.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings showing embodiments, but the scope of the present invention is not limited by these embodiments. FIG.
1 is a schematic cross-sectional view showing an embodiment of the exhaust pressure control device of the present invention, FIG. 2 is a schematic enlarged cross-sectional view taken along line XX of FIG. 1, and FIG. 3 is a schematic enlarged cross-sectional view taken along line YY of FIG. . In FIG. 1, the flow of the exhaust gas is from left to right in the figure. Therefore, in the following description, the left side of the drawing may be expressed as upstream, and the right side may be expressed as downstream.

As shown in FIG. 1, the exhaust pressure control device has an exhaust gas introduction section 1 connected to an extension of an exhaust pipe of an internal combustion engine, and extends downstream of the exhaust gas introduction section 1 and has an inner diameter. Is formed so as to expand at a predetermined angle toward the downstream, a maximum diameter portion 22 extending from the downstream end to the downstream side with the same diameter, and further tapered from the downstream end to the downstream side. An expansion chamber 2 surrounded by a diaphragm wall 31, a primary exhaust port 3 opening at the center of the downstream end of the expansion chamber 2, and an opening at an upstream edge (outer edge) of the diaphragm wall 31 at regular angular intervals. A secondary exhaust system flow path 5 having a secondary exhaust system inlet 4, the secondary exhaust system flow path 5 surrounding the throttle wall 31, and a downstream end of the secondary exhaust system flow path 5, Secondary exhaust system outlet 6 opening at regular angle intervals near the outside of the downstream end of primary exhaust port 3 Downstream of the outlet end of the primary exhaust port 3, a primary exhaust / secondary exhaust merging section 7 for merging exhaust gas passing therethrough and secondary exhaust passing the secondary exhaust system outlet 6, And a final rectification exhaust port 8 for finally discharging exhaust gas to the atmosphere on the downstream side.

Hereinafter, each part of the above exhaust pressure control device will be sequentially described in detail with reference to FIG. The exhaust gas introduction unit 1 is directly connected to an exhaust system of an internal combustion engine to which the exhaust gas introduction unit 1 is applied, and the inner diameter E is determined by the displacement of the internal combustion engine. The inner diameter E may be made to match the diameter of the discharge portion of the internal combustion engine to which the present invention is normally applied. Although not essential to the present invention, the exhaust gas introducing section 1 is provided with a number of holes formed in a cylindrical body constituting the exhaust gas introducing section 1 and the outer periphery thereof is surrounded by a sound absorbing material to muffle the sound. It shall be. Instead, a soundproof wall is provided on the outside to make it sealed,
Similarly, a configuration in which sound is muted may be adopted. Further, an exhaust gas purifying mechanism by a combination with a catalyst or the like may be appropriately combined.

The expansion chamber 2 has a diffusion wall surface 21 which expands with a diffusion angle F and diverges, and constitutes an expansion volume determined by the length A of the maximum diameter portion 22. The value of the diffusion angle F of the diffusion wall surface 21 and the value of the length A of the maximum diameter portion 22 are important factors that determine at what rate the exhaust gas that has passed through the exhaust gas introduction section 1 is expanded. When the diffusion angle F of the diffusion wall surface 21 is large and has a steep inclination, and the length A of the maximum diameter portion 22 is long, rapid expansion occurs. In this case, the state of the wave of the exhaust gas shows a wavefront waveform having a steep envelope as shown in waveform a in FIG. It has a gentle waveform like waveform b. This diffusion angle F is 2
It can be selected from 5 to 125 degrees, preferably from 30 to 120 degrees, according to the situation.

However, as described above in part, when the target internal combustion engine is to have high-speed characteristics, the diffusion wall 2
1, the diffusion angle F is increased, and the length A of the maximum diameter portion 22 is shortened to reduce the capacity of the expansion chamber 2. Thus, the discharge speed at the initial stage of the discharge is increased, the time until the back pressure is generated is shortened, and the generated back pressure is released in a short time. It is needless to say that the above procedure may be reversed when the target internal combustion engine has a low speed characteristic. The specific values are experimentally determined while assuming the above.

On the downstream side of the maximum diameter portion 22 of the expansion chamber 2, as described above, the primary exhaust port 3 narrowed down to the narrowest diameter after passing through the throttle wall 31 tapering with the throttle angle H. Is formed. The throttle angle H has a function of increasing the pressure again with respect to the traveling wave of the exhaust gas once expanded and decompressed in the expansion chamber 2, and the wave is transmitted through the exhaust gas introduction portion 1 to the internal combustion engine (not shown). It affects the engine side as back pressure.

Here, from the diffusion, expansion and decompression of the exhaust gas in the expansion chamber 2, the exhaust gas collides with the narrowed throttle wall 31, and further receives the compression action at the portion reaching the primary exhaust port 3. The phenomenon up to the occurrence of the generated back pressure pulse, as described above, affects the exhaust speed of the cylinder of the internal combustion engine, and has a significant significance in the effect of the device of the present invention. The specific range of the stop angle H of the stop wall surface 31 can be selected in a range of 25 to 125 degrees, preferably 30 to 120 degrees, according to the situation, like the diffusion angle F. The larger the throttle angle H, the faster and stronger the back pressure is generated.

The size and shape of the primary exhaust port 3 are determined by the volume of a unit pulse of exhaust gas which continuously proceeds in a pulsed manner. The volume of the unit pulse is determined by the displacement of the unit cylinder and the number of cylinders. The inner diameter J of the primary exhaust port 3 is selected to be smaller than the inner diameter E of the exhaust gas introduction unit 1. The length B of the primary exhaust port 3 is important for controlling the timing of the secondary exhaust, and should be selected according to the situation, but is selected to be at least equal to or larger than the inner diameter J. .

Specifically, the length B of the primary exhaust port 3 is configured to be short when the target internal combustion engine has a high speed characteristic, and is long when the internal combustion engine has a low speed characteristic. . The detailed value can be determined experimentally.

As shown in FIG. 1, the secondary exhaust system flow path 5 is provided outside a throttle wall 31 narrowed toward the downstream side by a predetermined throttle angle H and a secondary exhaust flow concentrically surrounding the throttle wall 31. It is formed by the space between the road wall 51. The exhaust gas flows into the secondary exhaust system flow path 5 via the upstream end of the throttle wall 31, that is, the secondary exhaust system inlet 4, which is a required number of through-holes opened at regular angular intervals in the outer edge. Will be Various configurations can be adopted for the opening form of the secondary exhaust system inlet 4. For example, as shown in FIG. 2, eight openings are arranged at a predetermined angle, for example, at a fixed angle interval of 45 degrees. can do. The total opening area of these secondary exhaust system inlets 4 is
It is determined to be equal to or less than the value obtained by multiplying the opening area of the primary exhaust port 3 by the number of cylinders (cylinders) of the target internal combustion engine.
Needless to say, when an exhaust pipe is provided for each cylinder even in the case of a multi-cylinder, it is the same as a single cylinder. Here, the opening area is the projected area of the opening as viewed along the flow direction of the exhaust gas (hereinafter, the opening areas have the same meaning).

The outflow of the secondary exhaust gas from the secondary exhaust system flow path 5 is performed via a secondary exhaust system outlet 6 formed on the downstream side. Various configurations can be adopted for the opening form of the secondary exhaust system outlet 6, for example, as shown in FIG.
A configuration in which four are arranged at a predetermined angle, for example, at an angle interval of 90 degrees can be adopted. These opening areas should be equal to or larger than those of the secondary exhaust system inlet 4.
In addition, these secondary exhaust system inlet 4 and secondary exhaust system outlet 6
The number, arrangement, dimensions, and the like of, can be adopted to configurations other than those exemplified here.

The primary exhaust / secondary exhaust merging section 7 surrounds the secondary exhaust stream exiting the secondary exhaust system outlet 6 around the central primary exhaust stream discharged through the primary exhaust port 3. Merge in such a way. In this case, both the primary exhaust gas and the secondary exhaust gas are exhausted by the differential pressure between the internal pressure of the apparatus and the atmospheric pressure, but the secondary exhaust gas is further accelerated by the Venturi effect due to the flow rate of the primary exhaust gas, and the secondary exhaust gas is discharged from the expansion chamber. The exhaust gas is discharged to the outside with a time lag from the primary exhaust gas.

In this case, the emission angle L of the primary exhaust is determined by the exhaust speed. The discharge angle L decreases as the exhaust speed increases, and increases as the exhaust speed decreases. The junction angle I of the secondary exhaust is important for efficiently discharging the secondary exhaust. It is selected from the same degree to the parallel degree corresponding to the emission angle L of the primary exhaust. It is to be noted that a sound deadening wall or other structure may be provided on the outer peripheral portion of the primary / secondary exhaust merging portion 7 and also a sound deadening effect may be expected.

The inner diameter K of the outlet of the final rectifying exhaust port 8
Is a diameter having a cross-sectional area equal to the total opening area (total projection area) of the secondary exhaust system outlet 6 and the primary exhaust port 3. The exhaust angle L of the final rectification exhaust port 8 equal to the emission angle L of the primary exhaust is
In the range of 2.5 to 40 degrees, preferably 3 to 30 degrees,
It should be determined appropriately according to the pumping speed. When the exhaust pressure control device of this embodiment is connected to an internal combustion engine and operated, an output improvement of approximately 15 to 20% is recognized over the entire rotation range.

[0035]

According to the exhaust pressure control apparatus of the present invention, by utilizing the energy possessed by the exhaust gas of the internal combustion engine, the exhaust state can be turned and the torque at the time of low speed operation can be increased. In addition, during high-speed operation, the back pressure is quickly released to increase the intake and exhaust efficiency, and as a result, it is possible to approach complete combustion. Therefore, it is possible to reduce the content of unburned components and at the same time reduce the emission of harmful oxides.

Its basic function is to expand and reduce the pressure in the exhaust gas expansion chamber while both the intake stroke and the exhaust stroke overlap for a very short time in the internal combustion engine.
The back pressure based on the pressure increase phenomenon that occurs again has a favorable effect on the intake and exhaust operations of the internal combustion engine.

At the moment when the exhaust valve is completely opened in the exhaust stroke of the internal combustion engine, the high-speed exhaust gas passes through the exhaust gas introduction section 1 in the shape of waveform a in FIG. To the room. At that time, the exhaust gas is expanded and decompressed, so that it assists in scavenging in the cylinder and, when the intake valve is subsequently opened, also assists in intake. Very slightly thereafter, the exhaust collides with the tapered throttle wall from the exhaust gas expansion chamber, and a compression action of the throttle wall toward the primary exhaust port occurs to generate a back pressure pulse, and this back pressure is superimposed. It functions to prevent new intake air from being unnecessarily exhausted through the open exhaust valve. Thereafter, high-speed exhaust is performed by the action of the primary exhaust port and the secondary exhaust system flow path, the exhaust gas expansion chamber is depressurized, and the emission of the next exhaust pulse is awaited.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of one embodiment of an exhaust pressure control device of the present invention.

FIG. 2 is a schematic enlarged sectional view taken along the line XX of FIG.

FIG. 3 is a schematic enlarged sectional view taken on line YY of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust gas introduction part 2 Expansion chamber 21 Diffusion wall surface 22 Largest diameter part 3 Primary exhaust port 31 Restricted wall surface 4 Secondary exhaust system inlet 5 Secondary exhaust system channel 51 Secondary exhaust channel wall 6 Secondary exhaust system outlet 7 Primary Exhaust / secondary exhaust junction 8 Final rectification exhaust port A Length of maximum diameter section  B Primary exhaust port length C Primary / secondary exhaust merging section length D Final straightening port length E Inner diameter of exhaust gas introduction section F Diffusion angle of diffusion wall G Maximum diameter of expansion chamber H Throttle angle of throttle wall I Secondary Exhaust confluence angle J Inner diameter of primary exhaust port K Inner diameter of final rectifier port L Primary exhaust emission angle (final rectified exhaust angle)

Claims (3)

[Claims] An exhaust gas introduction section connected to an exhaust system of an internal combustion engine, and at least a downstream side of a gas flow of the exhaust gas introduction section and an inner diameter gradually increases toward a downstream side. An exhaust gas expansion chamber surrounded by each of the diffusion wall and a throttle wall whose inner diameter is gradually reduced so as to be tapered toward the downstream at a further downstream side, and the throttle wall at a downstream side of the exhaust gas expansion chamber. A primary exhaust port opening at a tapered central portion, and a secondary exhaust system flow path formed outside the primary exhaust port opening at the center of the throttle wall, wherein the exhaust gas expansion occurs at an upstream edge of the throttle wall. A secondary exhaust system flow path that opens to the chamber and allows the exhaust gas to flow while gradually moving the exhaust gas toward the downstream central direction; an exhaust gas that has passed through the primary exhaust port and has passed through the secondary exhaust system flow path Secondary exhaust gas exits the secondary exhaust system A primary exhaust / secondary exhaust merging section through which the secondary exhaust gas which merges with the high-speed primary exhaust gas discharged from the primary exhaust port from the outer peripheral direction is sucked and merged. An exhaust pressure control device comprising: a secondary exhaust merging section; and a final exhaust rectifying section for discharging these exhaust gases to the outside at an appropriate flow rate. 2. The exhaust pressure control device according to claim 1, wherein a silencing mechanism is combined with the exhaust gas introduction section. 3. The exhaust pressure control device according to claim 1, wherein a silencing mechanism is combined with the primary / secondary exhaust junction.