JP2009024518A - Buffer device attached to exhaust system of reciprocal engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a buffer device which is compact and lightweight, and easily attached to an exhaust system of a reciprocal engine and capable of considerably damping the exhaust pulsation since large pulsation is present in the pressure and the flow rate in the exhaust system of the reciprocal engine, and not only the exhaust noise but also a catalyst device of the exhaust emission control are unfavorably affected. <P>SOLUTION: A branched pipe having the sufficiently large sectional area of a passage is arranged on the upstream side of a catalyst device or a muffler and on the downstream side of a manifold of an exhaust system. A flat plate-like container capable of smoothing the pulsation of the pressure by using the volumetric change caused by the expansion/contraction of a silicone rubber thin film is arranged at the position where the temperature of a terminating end of the branched pipe is ≤300°C as a buffer device of the pulsating pressure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

Industrial application fields

Automotive industry that requires environmental technology to prevent automobile exhaust noise and air pollution.

Technology background

On the other hand, automobile exhaust gas is cleaned by operating conditions and a catalytic device in terms of exhaust pollutant components, and a silencer is indispensable as a factor of exhaust noise, and its performance is also regarded as important. Many positive displacement engines have pulsation in the exhaust system, which influences the flow of exhaust gas in the catalyst device, and is considered to be a major factor of exhaust noise. Conventionally, an exhaust system has required a silencer and a catalyst device, but it has not been normally realized to attenuate pulsation upstream of the catalyst device. Innovative pulsation countermeasures have not been introduced just by maintaining the catalyst temperature and following conventional exhaust system technology, but the technology for attenuating pulsation in the exhaust system has advanced, so it is installed in ordinary automobiles. And the foundation for practical use was in place.

Shigeru Yanagihara et al., 19th Symposium on Internal Combustion B2-3; Pulsation damping buffer tube for intake and exhaust systems, 2007.09.09

High-temperature exhaust gas flows in the exhaust system of the engine, and it is assumed that the device is used within the limit of heat resistance. Further, the cause of the pulsation of the exhaust system is the actual volume flow rate in one direction and one cycle of the wave, and the buffer needs a capacity and capacity of volume change corresponding to the volume flow rate.
Although the position of the device and the temperature are also affected, the one-cylinder stroke volume of the engine is one target, and in order to achieve effective pulsation damping, 0.5L is required for gasoline engines, and 1 to 1.5L is recommended for diesel engines. It seems that a variable capacity of the container is necessary. It is a problem to ensure the heat resistance and variable capacity of the container.

  In the exhaust system, high-temperature exhaust gas reaching 350 ° C. or more and 600 ° C. flows at the position where the catalyst device or the like is disposed, but the average flow rate is zero in the side pipe branched from the exhaust pipe. Further, the temperature at a position that is not much higher than the branch point with a distance of 200 mm or more depends on the heat conduction of the tube wall and the cooling air, but can be kept at 300 ° C. or lower.

One of the means was a method of arranging a container of a buffer device having a restriction on heat resistance by selecting a condition of approximately 250 ° C. or less depending on the length, direction, and position of the branch pipe. In order to set the variable capacity of the container to 0.5 L or more, for example, an area of 160 cm ² or more was secured on the surface of the flat container, and the silicone rubber thin film was selected as the wall surface on the lower surface side of the container. The flow passage cross-sectional area of the branch pipe, the size of the container, the surface area and thickness hardness of the silicone rubber thin film attached thereto are appropriately selected in consideration of the cylinder volume of the engine.

Many automobile engines have 4 cylinders or 6 cylinders, but in the normal 4 cycles, there is one exhaust stroke every 2 rotations, and the gas in the cylinder flows out or exhausts from the exhaust valve to the exhaust pipe at almost equal intervals. .

As a result of this outflow, pulsations based on (number of cylinders) × (1/2 number of revolutions) exist in the exhaust pipe and move downstream. The assembly at a certain distance from the exhaust valve mainly becomes a pulsation of flow velocity and pressure corresponding to a periodic change in the discharge amount from each cylinder in the exhaust pipe portion. The cycle of pulsation is determined by the engine speed and the number of cylinders, but is affected by the flow resistance on the downstream side of the amplitude and the given amplitude on the upstream side, that is, one cycle and the unidirectional flow rate. It is important how much the damping effect of the device according to the invention contributes to the amplitude. This damping effect can be estimated from the relationship between the volume change and the internal pressure, i.e., static characteristics, when the container is closed, assuming that the flow resistance of the path from the branch pipe is almost negligible.

According to the present invention, the pulsation of the exhaust system can be effectively attenuated, but the degree of the effect varies depending on the average pressure influenced by the capacity of the apparatus and the position of the exhaust system to be mounted. Further, the effect differs depending on the comparison between the one-cycle fluctuation flow rate of the pulsation and the capacity of the apparatus. In a gasoline engine, even if the cylinder stroke volume is the same, the flow rate changes not only with the rotational speed but also with the load, so it is not possible to determine the damping effect.However, for example, the pulsation amplitude is reduced to 1/3 to 1 on the downstream side via a sub-muffler or catalyst. It is easy to suppress to / 4 or less.

One of the effects of the present invention is that, when mounted on the upstream side of the catalyst device, there is an effect of making the flow of exhaust gas on the catalyst carrier uniform, and the reaction efficiency can be improved. The pellet catalyst also has the effect of reducing wear. The monolith type has the effect of reducing the flow resistance by making the flow uniform, and the reaction efficiency can be improved even at the same temperature.

The effect of pulsation attenuation in the exhaust system according to the present invention is effective in suppressing automobile noise, and in particular, it is effective in acoustic attenuation in the low frequency region. Therefore, it is sufficient even if the conventional main muffler is downsized. There is a mute effect.

FIG. 1 schematically shows an example in which the buffer device of the present invention is mounted on an exhaust system.
A catalyst device or a pre-muffler 13 is disposed from an exhaust manifold 12 of the engine 11 via a collective exhaust pipe, and an exhaust pipe 14 is connected downstream thereof. A side pipe 15 is branched from the exhaust pipe 14 and connected to the flat buffer 1. At this time, as shown in FIG. 2, the flow is branched from the exhaust pipe 14 to the side pipe 15 so that the resistance is reduced and the smooth enlarged pipe 16 is formed. The heat-resistant bushing 9 is used to ensure a flexible joint.

As shown in FIG. 3, a heat-resistant silicone rubber thin film 3 is attached on the lower surface side of the housing 2 of the buffer 1 while maintaining airtightness, and a heat shield plate 22 is disposed on the vehicle body on the upper surface side, and the mounting bracket 7 is attached. Is loosely coupled to the car body. The rubber thin film 3 has a structure in which an O-ring is attached to the peripheral part, or a part of the peripheral part is made of a slightly thick silicone rubber plate of 0.6 mm or more, and has a thickness of about 0.4 mm or less while maintaining airtightness. To protect the silicone rubber film.

  A punching metal plate 5 through which outside air can freely enter and exit is disposed outside the rubber thin film 3 to protect and prevent obstacles applied to the rubber film from the outside. The casing 2 is provided with a flange 8 adapted to the rubber film 3, and the rubber film 3 is sandwiched between the corresponding flange 6 and the flange 8 integrated with the holding metal fitting 4 to which the punching metal 5 is attached. The periphery of the membrane 3 is tightened so as to ensure airtightness. The housing 2 is not only supported by the side pipe line 15 but also loosely coupled to the vehicle body by the mounting bracket 7. A heat shield plate 22 is disposed between the buffer 1 and the lower side of the vehicle body.

In the case of a four-wheeled vehicle, the exhaust system buffer device according to the present invention is arranged laterally to the exhaust pipe 14 between the pre-muffler and the main muffler, for example, when the exhaust system is arranged from the engine to the bottom of the vehicle body floor as shown in FIG. It arrange | positions as the buffer apparatus 1 through the pipe line 15. FIG. In the engine exhaust manifold 12, a pressure increase caused by exhaust gas outflow mainly from the exhaust stroke from each cylinder triggers pulsation in the pressure waveform. In the case of 4 cylinders, the main period of this pulsation is 4 periods for 2 revolutions, that is, 2 periods for 1 revolution. In the exhaust pipe 14 downstream of the pre-muffler 13, the pressure waveform is substantially sinusoidal (sine curve) with a considerably large amplitude as shown in FIG.

In the branch line 16, the average flow rate does not change, but most of the pulsation flow rate flows into and out of the side line 15, so that the pressure waveform amplitude in the exhaust pipe 17 on the front side of the main muffler is a as shown in FIG. This is much less than the case. This is the effect of exhaust gas flowing into the buffer 1 from the side pipe 15 or outflowing, but it is caused by the relationship between the static pressure of the buffer 1 and the volume change, unlike the Holm resonance box. This is due to the effect.

FIG. 5 shows a static relationship between the internal pressure when the buffer is sealed and the added or reduced volume (volume change). In FIG. 5, assuming that the actual volume pulsating flow in one direction (inflow or outflow) in one cycle is 300 cc and the average pressure is 0.8 kPa, the volume change range is 300 cc, which is about 600 cc as shown by the arrow range in the horizontal axis direction. It can be seen that the volume change corresponds to a pressure change of about 1 kPa and can be completely absorbed by the buffer 1. Actually, there is a pipe resistance, etc., and a slight amplitude remains as shown in FIG. Therefore, the capacity of the main muffler 18 is very small, and the use of the diffuser 19 that can reduce the resistance of the exhaust system is facilitated. In addition to reducing the weight of the exhaust system, it also relates to improving the fuel consumption rate due to the resistance reduction effect of the exhaust system.

Industrial potential

This apparatus may be widely used for pulsation attenuation in the suction system and the exhaust system of a fluid machine that generates pulsation such as a positive displacement pump. In particular, when a silencer is used, it will be advantageous in that it can be much smaller and lighter than the conventional shape. For example, when there is a need to mute in a limited space such as a two-wheeled vehicle, there is a high possibility that it will be used extremely heavily.

Schematic example in which the buffer device of the present invention is mounted on an automobile exhaust system Example of plan view of the buffer device of the present invention attached to an exhaust system Side elevation of the buffer device of FIG. Comparative example of pressure waveform when the buffer device of the present invention is exhausted / desorbed Example of pressure and volume change as static characteristics of the buffer device of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Buffer apparatus 2 Buffer apparatus housing | casing 3 Silicone rubber thin film 4 Holding metal fitting 5 Punching metal thin plate 6 Flange 7 Mounting bracket 8 Flange 9 Heat-resistant bush 10
DESCRIPTION OF SYMBOLS 11 Engine 12 Engine exhaust manifold 13 Premuffler 14 Exhaust pipe 15 Side pipe 16 Expansion branch pipe 17 Exhaust pipe 18 Main muffler 19 Diffuser 20
21 Heat insulation plate 22 Heat insulation plate

Claims (3)

  A branch pipe that is non-resonant and has a sufficient cross-sectional area is provided from the exhaust pipe downstream of the exhaust collecting pipe of the positive displacement internal combustion engine, and a part of the wall surface of the container in a direction and position at which the temperature can be kept at 300 ° C. or less at the tip. The expansion and contraction of the rubber thin film that makes up the exhaust gas makes it possible to change the volume and maintain airtightness, to form a container that can be mounted on an automobile, and thereby to absorb and attenuate pressure pulsations in the exhaust pipe system. Buffer device attached to the system   2. The buffer device according to claim 1, wherein an inlet cross section of the branch pipe from the exhaust pipe has an elliptical shape that is long in the exhaust pipe direction, the cross sectional area is increased, the flow path resistance is reduced, and the volume changing container is made flat. A buffer device attached to an exhaust system that facilitates the on-vehicle device and increases the surface area of the rubber thin film constituting the wall of the container.   3. A punching metal or a metal mesh that restricts expansion and contraction of a rubber thin film constituting a partial wall surface of the container in the buffer device according to claim 1 and protects damage from the outside and ensures circulation with outside air. A buffer device to be mounted on the exhaust system used for

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