JPH045416A - Two-stroke internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce NOx, HC and CO contained in exhaust gas efficiently by providing a catalytic converter rhodium located in an exhaust passage connected to an exhaust valve, and a catalytic converter oxidation located in an exhaust passage connected to an exhaust port. CONSTITUTION:A scavenging valve 2 and an exhaust valve 3 are attached to each of cylinder heads 4 respectively in respective cylinders of an engine body 1. A catalytic converter rhodium 12 is arranged in a first exhaust passage 11 located downstream from the exhaust valve 3 for performing deoxidation of NOx and oxidation of HC and CO contained in exhaust gas. In addition, a catalytic converter oxidation 14 is arranged in a second exhaust passage 13 located downstream from an exhaust port 7 for performing oxidation of HC and CO contained in the exhaust gas. The exhaust gas which contains a much amount of NOx in combustion gas is purified by the catalytic converter rhodium, and on the other hand, the exhaust gas which contains HC and CO mainly and is mixed with fresh air is purified by the catalytic converter oxidation. Thus, all of NOx, HC and CO contained in the exhaust gas can be reduced efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in two-stroke internal combustion engines, particularly in exhaust gas purification systems.

(Prior art) As a scavenging and exhausting system for two-stroke internal combustion engines, there is a so-called scavenging valve type uniflow one-way system in which fresh air is introduced from above the cylinder and exhaust gas is discharged from below the cylinder (Japanese Patent Laid-Open Publication No. 62-131.916, etc.).

These improve the scavenging and exhaust efficiency of two-stroke internal combustion engines,
By reducing the proportion of residual gas, irregular combustion is prevented and output is improved.

(Problem to be Solved by the Invention) However, in such a two-stroke internal combustion engine, the period during which the exhaust stroke and the scavenging stroke overlap is large, so compared to a four-stroke internal combustion engine, fresh air blows through. Even if a three-way catalyst is installed in the exhaust system to simultaneously reduce NOx and oxidize HC and CO to purify the exhaust,
The exhaust air-fuel ratio becomes diluted, making it impossible for the three-way catalyst to function effectively, and the NOx reduction efficiency in particular drops significantly.
It is becoming difficult to efficiently purify exhaust gas.

The present invention aims to solve such problems.

(Means for Solving the Problems) Therefore, the present invention provides an exhaust valve that opens at the beginning of the exhaust stroke, a scavenging valve that opens in the scavenging stroke after the exhaust valve closes, and a scavenging valve that opens near the bottom dead center of the piston to allow exhaust gas to flow out. The exhaust port is provided on the circumferential surface of the cylinder, a three-way catalyst is installed in the exhaust passage connected to the exhaust valve, and an oxidation catalyst is installed in the exhaust passage connected to the exhaust port.

The engine also includes a bypass passage that communicates the exhaust passages with each other upstream of the three-way catalyst and the oxidation catalyst, and a switching valve that opens the bypass passage in a high engine speed range.

(Function) When the exhaust valve opens in the latter half of the combustion stroke, only the exhaust that does not mix with fresh air flows from the exhaust passage to the three-way catalyst, and NOx in the exhaust is efficiently reduced and HC and Co are oxidized. .

When the exhaust port opens after the exhaust valve closes, the remaining exhaust gas flows from the exhaust passage to the oxidation catalyst, but at the same time, the scavenging valve also opens in overlap, so some of the introduced fresh air also flows out from the exhaust port. However, the exhaust gas flowing into the oxidation catalyst contains a large amount of oxygen, and HC and CO in the exhaust gas are efficiently oxidized.

In the high speed range of the engine, there is less fresh air blowing into the exhaust port, and the exhaust air-fuel ratio almost matches the air-fuel ratio of the combustion gas. At this time, the switching valve is opened to allow part of the exhaust gas from the exhaust port to also flow into the three-way catalyst, thereby reducing the exhaust pressure and purifying the exhaust gas.

(Example) Embodiments of the present invention will be described below based on the drawings.

As shown in FIGS. 1 and 2, each cylinder #1 of the engine body 1
~#6, a scavenging valve 2 and an exhaust valve 3 are each attached to the cylinder head 4, while the cylinder 5 has an exhaust port 7 that opens in a predetermined crank angle range centered on the bottom dead center of the piston 6. It is formed.

A supercharger 10 is installed in a scavenging passage 9 upstream of the scavenging valve 2, and pressurizes fresh air to the cylinders when the scavenging valve 2 opens.

The first exhaust passage 11 downstream of the exhaust valve 3 contains NO in the exhaust gas.
Two-way catalyst 12 that simultaneously reduces x and oxidizes HC and CO
An oxidation catalyst 1 is installed in the second exhaust passage 13 downstream of the exhaust port 7 to oxidize HC and CO in the exhaust gas.
4 will be installed.

Note that an expansion chamber 15 is provided upstream of the oxidation catalyst 14 to buffer exhaust pressure waves and improve air supply efficiency.

A bypass passage 16 is formed that connects the three-way catalyst 12 and the upstream side of the oxidation catalyst 14, and as shown in FIG. 4, the bypass passage 16 is fully closed in the low engine speed range and fully opened in the high engine speed range. A switching valve (rotary valve) 18 is interposed.

As shown in FIG. 3, the exhaust valve 3 opens in the latter half of the combustion stroke and closes before the exhaust port 7 opens, and the scavenging valve 2 opens at the same time as the exhaust port 7 opens, and the exhaust port 7 closes. It is set to close after a while.

In this embodiment, a fuel injection valve 2 that injects fuel into the cylinder during the compression stroke is installed in the cylinder head 4 together with a spark plug 20.
1 is installed.

As configured above, the operation will be explained next. Fuel is injected from the fuel injection valve 21 during the upward compression stroke of the piston 6, and the air-fuel mixture is ignited by the ignition plug 20 near the top dead center.

When the exhaust valve 3 is opened in the latter half of the combustion stroke in which the air-fuel mixture is ignited and combusted, combustion gas not mixed with fresh air flows from the first exhaust passage 11 to the three-way catalyst 12.

Since this combustion gas does not contain fresh air, it is maintained at a nearly stoichiometric air-fuel ratio, and the three-way catalyst 12 efficiently reduces NOx and oxidizes HC and Co in the exhaust gas. Particularly, since the high temperature combustion gas containing a large amount of NOx from above the cylinder flows out of the exhaust valve 3, the NOx purification efficiency is high.

When the exhaust port 7 opens after the exhaust valve 12 closes as the piston 6 descends, and the scavenging valve 2 opens at the same time, the exhaust port 7 opens.
As the remaining combustion gas begins to flow out, fresh air is introduced into the cylinder through the scavenging valve 2.

While this introduced fresh air expels the combustion gas in the cylinder, a part of it goes from exhaust bow 1 to exhaust bow 1 along with combustion gas.
It is discharged into the exhaust passage 13.

Therefore, the exhaust gas flowing into the oxidation catalyst 14 via the expansion chamber 15 becomes exhaust gas that is leaner than the stoichiometric air-fuel ratio containing fresh air (oxygen), and the HC and C○ in the exhaust gas are efficiently oxidized by the oxidizing atmosphere. Ru.

In this way, exhaust gas that does not contain fresh air and air that does contain fresh air are passed through separate exhaust passages 11.13, and those that do not contain fresh air are purified by the three-way catalyst 12, and those that do contain fresh air are purified by the oxidation catalyst 1-4. This allows each catalyst to function efficiently, and since the exhaust gas flowing to the three-way catalyst 12 is high-temperature combustion gas containing a lot of NOx above the cylinder, the overall NOx reduction is high. Effects can be obtained.

As shown in FIG. 4, the switching valve 18 of the bypass passage 16 is completely closed in the low engine speed range, but opens the bypass passage 16 as the engine moves to a high engine speed range.

For this reason, as the engine speed and load increase,
A part of the exhaust gas discharged from the exhaust port 7 after the exhaust valve 3 closes also flows into the primary catalyst 12 from the bypass passage 16.

In high rotation and high load ranges, the proportion of fresh air that blows through to the exhaust port 7 decreases, so the oxygen concentration in the exhaust decreases and approaches the stoichiometric air-fuel ratio, resulting in a sufficiently high level of purification even when the exhaust flows through the three-way catalyst 12. Efficiency can be gained.

In this way, in high engine speed and high load ranges where the exhaust flow rate increases, the exhaust gas is divided into the first exhaust passage 11 and the second exhaust passage 13, reducing the exhaust pressure and improving the output efficiency of the engine. be done.

Furthermore, since the two catalysts share the burden in the region where the exhaust flow rate is large, the required capacity of each catalyst can be reduced.

(Effects of the Invention) As described above, according to the present invention, exhaust gas containing a large amount of NOx in the combustion residue is purified by a three-way catalyst, and exhaust gas mixed with fresh air mainly containing HCCO is purified by an oxidation catalyst. Therefore, both NOx, HC, and C○ in the exhaust gas can be efficiently reduced. Furthermore, it is possible to prevent an increase in exhaust pressure in a high engine speed range and improve engine output.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIG. 2 is a plan view, FIG. 3 is an opening/closing characteristic diagram of a sweeping, exhaust valve, etc., and FIG. 4 is an opening/closing characteristic diagram of a switching valve. 1- Engine body, 2- Scavenging valve, 3... Exhaust valve, 5- Cylinder, 6... Piston, 7- Exhaust port, 1113
... Exhaust passage, 12. Three-way catalyst, 14. Oxidation catalyst, 16. Bypass passage, 18. Switching valve. Figure 2

Claims (2)

[Claims] 1. An exhaust valve that opens at the beginning of the exhaust stroke, a scavenge valve that opens during the scavenge stroke after the exhaust valve closes, an exhaust port that opens near the bottom dead center of the piston to allow exhaust to flow out, and an exhaust valve. A two-stroke internal combustion engine characterized by comprising a three-way catalyst installed in an exhaust passage connected to an exhaust port, and an oxidation catalyst installed in an exhaust passage connected to an exhaust port. 2. 2. The two-stroke internal combustion engine according to claim 1, further comprising a bypass passage that communicates the exhaust passages with each other upstream of the three-way catalyst and the oxidation catalyst, and a switching valve that opens the bypass passage in a high engine speed range.