JPH0378528A - Two-stroke internal combustion engine - Google Patents

Abstract

PURPOSE:To improve purifying performance of exhaust by providing constitution in such a way as providing an exhaust control valve, turnable in a vertical direction, in the upper edge part of an exhaust port, opened and closed by a piston, and guiding only combustion gas, just after the exhaust port is opened, to a catalyst device simultaneously with a variable control in the open timing of the exhaust port. CONSTITUTION:In an exhaust port 15, opened and closed by a piston 7, in a side surface of a cylinder liner 5 of a two-stroke engine, an exhaust control valve 18, set to an upper position in a high speed high load region, is vertically turnably arranged in an upper edge part of the exhaust port 15. The point end of a valve unit 18b of this exhaust control valve 18 is formed in a circular arc surface 18c connected to an upper end edge in an opening part of the exhaust port 15, and a subexhaust port 19 is open-formed in this circular arc surface 18c. A subexhaust passage 20, which communicates with this subexhaust port 19, is formed in the valve unit 18b, and this subexhaust passage 20 can be connected to the first exhaust passage 21 provided with an exhaust purifying catalyst device. While the exhaust port 15 is connected to the second exhaust passage 22 which joins the first exhaust passage 21 in the downstream side of the catalyst device.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an improvement in a two-stroke internal combustion engine of the port scavenging type in which a piston opens and closes a scavenging port and an exhaust port opened on the side of the cylinder.

Conventional Technology In a two-stroke internal combustion engine in which a piston opens and closes a scavenging port and an exhaust port that open on the side of the cylinder, the piston moves to a predetermined position (usually ATDC 90°) after an explosion.
When the cylinder has descended to the front and back), the exhaust port is opened and combustion gas starts to be discharged due to the pressure inside the cylinder. When the piston further descends to the next predetermined position (usually around 120° ATDC) and the scavenging port is opened, fresh air compressed in the crank chamber flows into the combustion chamber and scavenges the remaining combustion gas. The cylinder is filled with water. When the piston starts to rise, the scavenging port closes first, and then the exhaust port closes, completing the gas exchange.

Two-stroke internal combustion engines like this have the disadvantage of high HC emissions because some of the fresh air that flows in from the scavenging port blows through to the exhaust port, so a catalyst device in the exhaust system is essential. becomes.

In this case, while the combustion gas at the beginning when the exhaust port is open is sufficiently high temperature, the combustion gas discharged at the later stage when the piston has lowered considerably becomes low temperature, which lowers the temperature of the catalyst. Because of this problem, conventionally,
In JP-A-64-19108, the exhaust port is divided into upper and lower parts, and only high-temperature exhaust gas is introduced into the catalyst device from the upper exhaust port, and the exhaust gas exiting from the lower exhaust port is directed downstream of the catalyst device. Some are designed to guide you.

Furthermore, two-stroke internal combustion engines are known to have a problem in which scavenging efficiency decreases in low speed and low load regions, resulting in unstable combustion and a decrease in output.

In order to deal with this problem, there are conventional exhaust control valves that are arranged at the upper edge of the exhaust port to change the opening and closing timing of the exhaust port (for example, Japanese Patent Laid-Open No. 62-23523
Publications, etc.). With this type, the actual opening/closing timing of the exhaust port is determined by the lower edge of the tip of the valve body, so by controlling the exhaust control valve to the lower position on the low speed and low load side, the opening timing of the exhaust port is delayed and the low speed torque is increased. It is possible to improve the fuel efficiency and stabilize combustion.

Problems to be Solved by the Invention However, when this exhaust control valve is applied to the above-mentioned upper and lower divided exhaust port, when the exhaust control valve is positioned downward to delay the opening timing of the exhaust port, the catalyst There is a risk that the amount of exhaust gas introduced into the device will be extremely small, and most of the combustion gas will be exhausted from the lower exhaust port without passing through the catalyst device.

Means for Solving the Problems According to the present invention, the initial high-temperature combustion gas is guided to the catalyst device through the inside of the valve body of the exhaust control valve. That is, the present invention provides a two-stroke internal combustion engine that is equipped with a scavenging port that opens on the side of the cylinder and an exhaust port that also opens on the side of the cylinder, and in which both ports are opened and closed by a piston. An exhaust control valve is provided that rotates in the vertical direction to cover a part of the exhaust port, and a sub-exhaust port is formed at the tip of the valve body of the exhaust control valve, and a sub-exhaust passage is formed inside the valve body. The auxiliary exhaust passage is characterized in that it is formed through the exhaust passage and that a catalyst device is provided on the downstream side of the auxiliary exhaust passage.

In the above structure, when the piston descends after the explosion, the sub-exhaust port of the exhaust control valve opens first, and comparatively high-temperature, high-pressure combustion gas is guided to the catalyst device through the sub-exhaust passage within the valve body. When the piston descends further, the exhaust port below the exhaust control valve opens and combustion gas, which has cooled to a certain degree, flows out, but it is exhausted without passing through the catalyst device.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a sectional view of a two-stroke internal combustion engine according to the present invention, in which a crankcase cover 2 is fixed to the lower part of a cylinder block l with bolts 3 to form a sealed crank chamber 4, and a cylinder A separate cylinder liner 5 is attached to the cylinder liner 5 by press-fitting or the like, and a cylinder head 6 closes the upper end of the cylinder liner 5.

7 is a piston that slides inside the cylinder liner 5;
9 is a crankshaft housed in the crank chamber 4;
is a connecting rod that connects the two.

An intake port 10 connected to the crank chamber 4 is provided with a reed valve 11 that prevents fresh air flowing into the crank chamber 4 from flowing backward.

The cylinder head 6 also includes a fuel injection valve 1 that injects fuel toward a combustion chamber 12 defined by a piston 7.
3 and a spark plug 14 are installed.

On the side surface of the cylinder liner 5, an exhaust port 15 and a scavenging port 16, which are opened and closed by the piston 7, are formed in a substantially rectangular shape. The scavenging port 16 communicates with the crank chamber 4 via a scavenging passage 17.

An exhaust control valve 18 made of a valve body tsb fixed to a rotating shaft 18a is disposed at the upper edge of the exhaust port 15. This exhaust control valve 18 is configured to be able to rotate up and down about a rotation shaft 18a at the end, and an arcuate surface 18c continuous to the upper edge of the opening of the exhaust port 15 is formed at the tip of the valve body 18b. The upper part of the exhaust port 15 is partially covered.

Also, there is a sub-exhaust port on the tip arc surface 18c of the valve body 18b! 9 is formed as an opening, and a sub-exhaust passage 20 is formed from this sub-exhaust port 19 through the inside of the valve body 18b. This auxiliary exhaust passage 20 is connected to a first exhaust passage 21 that is provided with a catalyst device for purifying exhaust gas at a downstream position (not shown).

And an exhaust port that opens below the exhaust control valve 18!
5 is connected to the second exhaust passage 22.

This second exhaust passage 22 joins the first exhaust passage 21 on the downstream side of the catalyst device. Alternatively, the configuration may be such that the exhaust gas is guided to the outside separately from the first exhaust passage 21.

As shown in FIG. 2, the rotating shaft 18a of the exhaust control valve 18 passes through the exhaust port 15, and an actuator 22 such as a servo motor is linked to one end of the rotating shaft 18a. Note that 23 is a sealing member. The actuator 22 is controlled by a control signal output from a control circuit 24. The control circuit 24 receives an engine rotational speed signal detected by a crank angle sensor (not shown) and a load signal detected by an air flow meter, etc., and optimizes the exhaust control valve 18 based on these signals. It is designed to control the position.

That is, the basic control characteristic of the exhaust control valve 18 is that it is controlled upward in the high-speed, high-load range, that is, toward the top dead center.
At low speed and low load, it is gradually controlled downward, that is, toward the bottom dead center (see Fig. 3).

Discharge of the combustion gas after the explosion starts when the top ring 25 of the piston 7 falls below the upper edge of the auxiliary exhaust port 19 of the exhaust control valve 18. Note that this actual exhaust port opening timing is set around 90° ATDC in the high speed, high load range where the exhaust control valve 18 is located at the uppermost position, and is naturally delayed from this in the low speed and low load range. It becomes something.

Immediately after the sub-exhaust port 19 is opened by the downward movement of the piston 7, the combustion gas is at a considerably high temperature.

It is in a high pressure state, and is led to the catalyst device through the auxiliary exhaust passage 20 and the first exhaust passage 21 inside the exhaust control valve 18. Therefore, the catalyst device is kept at a sufficiently high temperature, and HC and the like contained in the exhaust gas can be effectively treated.

Further, when the piston 7 moves further down, the exhaust port 15 below the exhaust control valve 18 is opened. Also, around this time, the scavenging port I6 is opened and compressed fresh air is supplied from the crank chamber 4 to scavenge the residual combustion gas in the cylinder, so the temperature of the combustion gas drops rapidly at this stage. However,
Most of the combustion gas that has become low temperature in this way is at exhaust port 1.
5 through the second exhaust passage 22. Therefore,
It does not pass through the catalytic device and its temperature drop is avoided.

The effect of separating the early high temperature combustion gas and the latter low temperature combustion gas as described above is performed regardless of the rotational position of the exhaust control valve 18. That is, as shown in FIG. 3, even if the exhaust control valve 18 is located downward, the high-temperature combustion gas discharged in the early stage is always guided to the catalyst device through the sub-exhaust port 19, and the low-temperature combustion gas in the latter stage is always guided to the catalyst device through the sub-exhaust port 19. is the second exhaust passage 2
You will be guided to the second side.

Effects of the Invention As is clear from the above explanation, in the two-stroke internal combustion engine according to the present invention, at the same time as variable control of the exhaust port opening timing, only the high temperature combustion gas immediately after the exhaust port is opened is reliably guided to the catalyst device. can do. Therefore, it is possible to stably clean the exhaust gas while improving the scavenging efficiency in the low speed and low load range.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a two-stroke internal combustion engine according to the present invention, FIG. 2 is a sectional view of its main parts, and FIG. 3 is an explanatory diagram showing the operating state in a low speed and low load range. . 7...Piston, 15...Exhaust port, 16...
Scavenging port, 18... Exhaust control valve, 18b... Valve body, 19... Sub-exhaust port, 20... Sub-exhaust passage. Figure 2 Figure 1

Claims (1)

[Claims] (1) In a two-stroke internal combustion engine that is equipped with a scavenging port that opens on the side of the cylinder and an exhaust port that also opens on the side of the cylinder, and in which both ports are opened and closed by a piston, the upper edge of the exhaust port is placed in the vertical direction of the cylinder. An exhaust control valve that rotates to cover a part of the exhaust port is provided, and a sub-exhaust port is formed at the tip of the valve body of the exhaust control valve, and a sub-exhaust passage is formed penetrating inside the valve body. A two-stroke internal combustion engine, further comprising a catalyst device provided downstream of the sub-exhaust passage.