JPS5919784Y2 - Internal combustion engine exhaust passage device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust passage device that utilizes pulsations in the exhaust pressure of an internal combustion engine to introduce secondary air into an exhaust system.

Various devices have been proposed in the past that utilize pulsations in exhaust pressure to draw in and mix secondary air for purifying exhaust gas into exhaust gas.

A conventional system of this type is shown in FIG. 1, for example.

That is, a catalytic converter 4 loaded with an oxidation catalyst is connected to an exhaust manifold 2 of an internal combustion engine 1 via a front tube 3, and a muffler 6 is connected downstream of this converter 4 via a center tube 5. The rear tube 7 connected to the downstream end of the tube 6 is opened to the atmosphere.

A secondary air inlet (not shown) provided in the exhaust manifold 2 and a check valve 9 provided in the air cleaner 8 of the engine 1 are communicated and connected via a secondary air inlet passage 10 equipped with an air gear rally. When the inside of the exhaust manifold 2 becomes negative pressure due to blowdown, secondary air is sucked into the exhaust manifold 2 from the air cleaner 8 through the check valve 9 and the secondary air introduction passage 10, and the secondary air and the exhaust are mixed. and unburned components of the exhaust gas are reacted in a catalytic converter 4 to purify the exhaust gas.

(Refer to Japanese Unexamined Patent Publication No. 52-34120).

However, in this type of exhaust gas purification system, secondary air is inherently insufficient, although it is mixed in by suction action due to pulsation of exhaust pressure, compared to systems that forcibly supply secondary air using an air pump or the like. There are concerns that this will happen.

In other words, the magnitude of the negative pressure induced by the pulsation of exhaust pressure depends on the cycle of exhaust blowdown, which is determined by the rotational speed of the engine, and the length of the exhaust pipe (the distance from the exhaust valve to the point where the pipe cross section suddenly expands). The negative pressure level is highest in a resonant region where the period of air column vibration coincides with the determined period, and conversely, the negative pressure level becomes extremely small in a non-resonant region where the phase of the period is reversed.

Therefore, the characteristic of the amount of secondary air introduced relative to the engine rotational speed is large in the resonance region and small in the non-resonance region, so that the curve always has peaks and troughs, as shown by the broken line in FIG.

Therefore, in the operating range where the valley occurs, the introduction rate of secondary air is extremely reduced, resulting in a shortage of secondary air, and the conversion efficiency of the oxidation catalyst is extremely reduced, resulting in the disadvantage that the desired exhaust purification function cannot be achieved. there were.

In order to eliminate these drawbacks, move the catalytic converter or muffler position, change the length of the exhaust pipe,
It may be possible to make the secondary air introduction curve as flat as possible for the engine rotation speed so that there is no large valley in the secondary air introduction curve, but due to the layout of a normal vehicle, the catalytic converter and muffler Changing the position is often virtually impossible and impractical.

Therefore, in such cases, the amount of secondary air is increased by increasing the number of check valves or changing the length of the secondary air introduction passage, but these methods essentially cause a shortage of secondary air. It cannot be resolved.

By the way, in the above-mentioned publication, in order to eliminate the secondary air shortage, the front tube is made to have a larger cross-sectional area than the center tube on the downstream side of the exhaust pipe, thereby making the tuning (resonance) points of the air column vibration in the exhaust pipe mutual. A measure is adopted to reduce the influence of the out-of-tuning point and increase the amount of secondary air supply by bringing the air temperature close to .

However, this goes against the general tendency of arranging the front tube to have a larger diameter than the center tube in response to the exhaust temperature, so the back pressure increases and the scavenging efficiency and intake air filling are affected. There is a risk that efficiency will decrease and output will likely deteriorate.

Although the points tuned to the two natural frequencies of the front tube and center tube (same order) are simply shifted relative to the engine speed, the number of tuning points remains the same.
If there is a non-tuning point between the next vibration orders (first order and second order), there is a risk that the influence of the non-tuning point will be increased.

The present invention was made in view of these circumstances, and
Even if it is not possible to change the position of the catalytic converter or muffler due to the layout of the vehicle, an extremely simple configuration can create a new engine rotation speed that synchronizes with the cycle of air column vibration, thereby reducing the amount of secondary air introduced. The aim is to increase the

Hereinafter, the present invention will be explained in detail based on the embodiments shown in FIGS. 2 to 10.

In the first embodiment shown in FIGS. 2 to 4,
A catalytic converter 4 is connected to an exhaust manifold 2 of an internal combustion engine 1 via a front tube 3.

A honeycomb-shaped or pellet-shaped oxidation catalyst 4' is loaded inside the catalytic converter 4, and a muffler 6 is connected downstream of it via a center tube 5, and a rear tube 7 connected to this muffler 6 is connected to the muffler 6 via a center tube 5. It is open to the atmosphere.

Further, the other end of the secondary air introduction passage 10, whose one end is connected to the check valve 9 provided with the air cleaner 8 of the engine 1, is merged into the exhaust system passage at the exhaust manifold 2, as in the conventional case. It is.

In such an exhaust purification system, as shown in FIGS. 3 and 4, a horizontally long expansion chamber 11 having a substantially square shape on 1000 sides is interposed at the connection between the catalytic converter 4 and the center tube 5. There is.

The expansion chamber 11 has an inlet and an outlet area (a-a
'.

c-c') are made approximately equal, and the central part is the cross section a-a'
Alternatively, it is constructed of a hollow container having a cross-sectional area (bb') larger than c-c', but as in the second embodiment shown in FIG. 11 may be integrally molded, or, although not shown, may be integrally molded at the upstream portion of the muffler 6.

Further, the number of expansion chambers 11 does not necessarily have to be one, and the number of expansion chambers 11 is not limited to one.
A plurality of expansion chambers 11 may be connected and integrated as in the third embodiment shown in the figure, or a part of the center tube 5 may be made into a hollow container as in the fourth embodiment shown in FIG. Alternatively, as in the fifth embodiment shown in FIG. 8, a tube 5' branched from the center tube 5 may be used. The tip may be opened to the expansion chamber 11, or, although not shown, a portion of the center tube 5 may be expanded and expanded.

As mentioned above, in such a configuration, the amount of secondary air introduced reaches its peak value at the length of the exhaust pipe system that is synchronized with the rotational speed of the engine (the length from the exhaust valve to the position where the pipe cross section suddenly expands). That's right.

Furthermore, according to acoustic theory, the relationship between the tuned engine rotational speed N at which the amount of secondary air introduced reaches its peak and the length l of the exhaust pipe system is as follows:
In the case of a 4-cylinder engine, N = 15 C/2 n, 1 (C: in the exhaust pipe (
7) Sound speed, n=1. 2. 3...).

Therefore, if we assume that the length to the inlet of the catalytic converter 4 is 11, the length to the inlet of the expansion chamber 11 is 12, and the length to the inlet of the muffler 6 is 13, then Engine rotation speed N1. N2. A peak in the amount of secondary air introduced occurs at each rotation N3, a new peak in the amount introduced at the N2 rotation, and as shown by the solid line in FIG. 9, the amount of introduced secondary air increases.

Further, when the expansion chambers 11 are connected as shown in FIG. 6, the length lA up to the entrance of each expansion chamber 11.

Since peak values are also obtained at rotational speeds NA, NB, and No that are synchronized with lB and lo, the secondary air introduction characteristics are further flattened as shown by the dashed line in FIG.

Therefore, the more expansion chambers 11 are provided, the more effective it is.

On the other hand, the influence of the engine displacement and the volume of the expansion chamber 11 on the amount of secondary air introduced is as shown in FIG.
If the volume of the expansion chamber 11 is less than 50% of the exhaust volume, the amount of introduced air will increase rapidly as the volume of the expansion chamber 11 increases.
% or more, it increased moderately.

Therefore, the volume of the expansion chamber 11 should be set at least 5 times the engine displacement.
It is effective to set it to 0% or more.

As described above, the present invention has an extremely simple configuration in which an expansion chamber of a predetermined volume is provided between the catalytic converter and the muffler in the exhaust system path downstream from the confluence point of the secondary air and the exhaust gas. However, since it is possible to create a new peak in the amount of secondary air introduced without changing the position of the catalytic converter or muffler, it is possible to prevent the occurrence of operating regions where the amount of secondary air is insufficient as in the past. Since the conversion efficiency of the oxidation catalyst can be maintained at a high level, the exhaust purification function can be improved.

[Brief explanation of the drawing]

Fig. 1 is an overall view showing an example of a conventional secondary air introduction system, Fig. 2 is an overall view showing a first embodiment of the present invention, Fig. 3 is a plan view of the main parts of the same, and Fig. 4 is a general view showing an example of a conventional secondary air introduction system. 3 is a front view, FIG. 5 is a cross-sectional view of the main part showing the second embodiment, FIG. 6 is a cross-sectional view of the main part showing the third embodiment, and FIG. 7 is a main part showing the fourth embodiment. FIG. 8 is a schematic sectional view of the main parts showing the fifth embodiment,
Figure 9 is a diagram of the relationship between the engine rotation speed and the amount of secondary air introduced.
FIG. 10 is a diagram showing the relationship between the volume of the expansion chamber (engine displacement) and the amount of secondary air introduced. 1...Internal combustion engine, 2...Exhaust manifold, 3...Front tube, 4...
・Catalytic converter, 5...center tube,
6...Muffler, 7...Rear tube, 8...Air cleaner, 9...Check valve, 10...Secondary air introduction Aisle, 11...
- Expansion chamber.

Claims (5)

[Scope of utility model registration request] (1) In an exhaust purification system for an internal combustion engine that includes a secondary air introduction device that supplies secondary air to the exhaust system using pulsations in exhaust pressure, a catalytic converter loaded with an oxidation catalyst, and a muffler, An exhaust passage device for an internal combustion engine, characterized in that an expansion chamber of a predetermined volume is provided between a catalytic converter and a muffler downstream of a confluence point of secondary air and exhaust gas. (2) The exhaust passage device for an internal combustion engine according to claim 1, wherein the expansion chamber is formed to have a volume that is at least 50% of the engine displacement. (3) The exhaust passage device for an internal combustion engine according to any one of claims 1 to 2, wherein the expansion chamber is divided into a plurality of chambers. (4) The expansion chamber is formed by covering a part of the exhaust pipe with a hollow container, and communicating the front and rear ends of the hollow container with the inside of the exhaust passage. The exhaust passage device for an internal combustion engine according to any one of Item 3. (5) The exhaust passage device for an internal combustion engine according to any one of claims 1 to 3, wherein the expansion chamber is integrally formed with a catalytic converter.