JPS5815615Y2 - Catalytic exhaust system for multi-cylinder internal combustion engines for motorcycles - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a catalytic exhaust system for a multi-cylinder internal combustion engine for a motorcycle, in which a muffler provided with a catalyst is connected to each exhaust pipe led out from each cylinder.

Generally, a two-cylinder multi-cylinder internal combustion engine installed in a motorcycle has an independent exhaust pipe connected to each cylinder.

The downstream ends of these exhaust pipes are each connected to a muffler.

By the way, as an exhaust purification measure, it is widely adopted to install a warm-up catalyst in the exhaust pipe to purify the exhaust mainly during warm-up operation, and a method to install a catalyst in the muffler to purify the exhaust mainly during normal operation. If the exhaust pipes are installed independently from each other, if the engine misfires during normal operation, a large amount of unburned gas will flow through the exhaust pipe to the muffler connected to the misfired cylinder. As a result of combustion near the muffler, a large thermal load is applied to the catalyst in the exhaust pipe connected to the cylinder, resulting in severe deterioration.

Also, if each exhaust pipe is independent for each cylinder,
Each exhaust pipe bears a large amount of exhaust gas only when exhausting from that cylinder, and takes a break when exhausting other cylinders, so the catalyst must intermittently purify a large amount of exhaust gas. Therefore, it must be made larger.

On the other hand, it is desired to increase the exhaust gas purification efficiency during warm-up operation with a simple configuration.

This idea was made based on these circumstances,
The simple configuration increases exhaust purification efficiency during warm-up operation, while reducing thermal deterioration of the muffler catalyst connected to the relevant cylinder in the event of a misfire during normal operation, while reducing and continuing the exhaust volume connected to each catalyst. An object of the present invention is to provide a catalytic exhaust system for a multi-cylinder internal combustion engine for a motorcycle, in which the catalyst can be made smaller by bringing the catalyst into contact with the catalytic converter.

An embodiment of this invention will be described below based on the drawings.

In the figure, 1 is a two-stroke, two-cylinder engine mounted on a motorcycle, and exhaust pipes 3, 3 are connected to the exhaust holes of each cylinder 2, 2.

These exhaust pipes 3.3 are collected into one pipe at positions close to the cylinders 2, 2, and are branched into two pipes 5, 5 again from this collection part 4 on the exhaust rear side.

A muffler 6.degree. 6 is connected to each of these branch portions 5,5.

The muffler 6.6 each has a nine-shaped expansion chamber 7 that widens at the end.
．． A muffling chamber 9, 9 (only one is shown) is provided behind the muffling chamber 7, and main catalysts 8, 8 are provided upstream of the muffling chamber 9, 9.

Note that the silencing chamber 9 is composed of a plurality of expansion chambers 10... and a throttle passage 11 that communicates these expansion chambers 10.

The gathering portion 4 is shaped like a substantially straight tube, and has a warm-up catalyst 13 in the form of a fiber, for example, fixed to its inner wall surface.

A secondary air suction pipe 14 is also attached to this collecting part 4, and communicates the inside and outside of the collecting part 4.

Note that this suction pipe 14 is provided with a check valve 15 that blocks exhaust from inside the gathering portion 4 and only allows intake of outside air.
Moreover, an air cleaner 16 is connected to the outside of this check valve 15.

According to such a configuration, during warm-up operation, exhaust gas is alternately sent from each cylinder 2, 2 to the collecting part 4 via the exhaust pipes 3, 3, and therefore, the collecting part 4 Since the warm-up catalyst 13 provided in the reactor receives the heat of the exhaust gas that alternately drifts, the temperature rises to the reaction starting temperature extremely quickly.

Therefore, the exhaust gas purification efficiency during warm-up operation is increased.

Furthermore, during normal operation, the exhaust gas alternately sent from each cylinder 2.2 passes through the collecting section 4, is almost evenly distributed at the branching sections 5, 5, and is almost continuously sent to the muffler 6.
．． 6, the exhaust gas discharged from one cylinder 2 will eventually be purified by the main catalysts 8, 8 of both mufflers 6 and 6, resulting in high purification efficiency and
Since each main catalyst 8, 8 only needs to purify half of the exhaust gas from one cylinder 2, its surface area can be reduced, and the main catalysts 8, 8 can be made smaller.

If a misfire occurs in the cylinder 2 on one side, the combustion gas will pass through the collecting section 4 and branch sections 5 and 5.
Since the power is divided into roughly half and flows into the muffler 6.6 and is combusted within each muffler 6.6, each muffler 6.6 ends up absorbing half of the unburned gas discharged from one cylinder 2. As a result, the heat load on the main catalysts 8.8 is reduced, and thermal deterioration of these main catalysts 8.8 is reduced.

Note that the unburned components of fuel remaining in the exhaust gas are removed from the exhaust pipe 3.
, 3 to the muffler 6.6, but at this time, if the amount of air in the exhaust is small, the secondary air intake pipe 14
Outside air is taken in through the

First, since the negative pressure of the exhaust pulsating wave acts inside the suction pipe 14, outside air is sucked in through the air cleaner 16 button and the check valve 15, thereby replenishing the air necessary for the above-mentioned combustion.

In this case, if the suction pipe 14 is connected to the gathering part 4, the suction pipe 14
Only one will be enough.

As explained above, in this design, the exhaust pipes led out from each cylinder are once collected at a position upstream of the catalyst, so that during normal operation, the exhaust from each cylinder once passes through the collection part. Afterwards, it will be distributed almost equally to each muffler, and the amount of exhaust that comes into contact with the catalyst in each muffler will be small. Secondly, each catalyst will be continuously fed with exhaust gas from all cylinders alternately. Since it comes into contact with the exhaust gas and can therefore reduce the reaction capacity of the catalyst, it is possible to downsize the catalyst.

In addition, even if a misfire occurs in any one cylinder or cylinder, the unburned gas is distributed to each muffler and burned, so the heat load is distributed to all catalysts, so the heat load on each catalyst is reduced. This has the effect of reducing thermal deterioration of each catalyst and extending its life.

In addition, since we installed a warm-up catalyst in the collecting part, it receives the heat of the exhaust gas that alternately flows in from all the cylinders, and the rise to the reaction starting temperature is extremely quick, so a special configuration is required. Even if it is not used, the exhaust gas purification efficiency during warm-up operation will be increased.

[Brief explanation of drawings]

The drawings show one embodiment of this invention, and Fig. 1 is a partially sectional front view showing the exhaust pipe assembly section for a two-cylinder engine;
FIG. 2 is an enlarged sectional view of the exhaust system. 1...Engine, 2...Cylinder,
3...Exhaust pipe, 4...Collection part, 5...
...Branch, 6...Muffler, 8...
・・Main catalyst, 9・・・・Sound reduction chamber, 13・・・・
Warm-up catalyst, 14... Suction pipe.

Claims (1)

[Scope of utility model registration request] In a multi-cylinder internal combustion engine for motorcycles in which a muffler equipped with a catalyst is connected to each exhaust pipe led out from each cylinder, the exhaust pipes are once gathered at one place upstream of each of the catalysts, and A catalytic exhaust system for a multi-cylinder internal combustion engine for a motorcycle, characterized in that a warm-up catalyst is installed in the collecting part.