JPH072978Y2 - 2-cycle internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a two-cycle internal combustion engine in which a cylinder head is provided with a fresh air valve and an exhaust valve.

[Conventional technology]

In Japanese Patent Laid-Open No. 53-46516 and Japanese Patent Publication No. 60-5770,
An open chamber two-stroke internal combustion engine having an intake (fresh air) valve and an exhaust valve is disclosed. In this two-cycle internal combustion engine, when the piston is at the bottom dead center, the intake valve and the exhaust valve are opened almost at the same time, and the fresh air flowing from the intake valve is directed downward and is inverted at the top surface of the piston to move inside the cylinder. To form a vertical U-shaped flow.
The interface between the fresh air and the exhaust is first near the intake valve, then in the lower center of the cylinder, and then towards the exhaust valve, so that exhaust and fresh air replaces the entire cylinder. Has become.

However, although such a two-cycle internal combustion engine has no problem in the high load range, it has a problem in combustion at the idle time or in the light load range. At idle or in a light load area, the amount of fresh air supplied is small and a large amount of exhaust gas remains in the cylinder.Therefore, the fresh air is dispersed and thinned in the residual exhaust gas, and the fresh air is ignited by the cylinder head. Cannot be collected near the plug. That is, in the U-shaped flow in the cylinder in the vertical direction,
This is because the mainstream of fresh air moves below the cylinder. For this reason, ignition due to the ignition plug provided in the cylinder head, the generation of flame kernels is hindered, and the flame propagation speed decreases, so that misfire or combustion fluctuation easily occurs.

Further, it has been publicly known to form a swirl around the cylinder axis in the intake air. For example, U.S. Pat.
No. 928 supplies air from two intake valves arranged opposite to each other to form a swirl around the cylinder axis. The exhaust valve is arranged in a sub chamber formed in the center of the top of the cylinder. Therefore, in the internal combustion engine disclosed in this patent, combustion is started in the sub chamber and then spreads into the swirling cylinder, which causes swirl in the exhaust gas or residual exhaust gas. It does not stratify between gas and fresh air.

The applicant of the present application has previously described that when the load including the idle is low, a part of the exhaust gas discharged from the exhaust port when the exhaust valve is opened is re-injected into the combustion chamber while being swirled around the cylinder axis, so that the piston We proposed a two-cycle internal combustion engine that can perform stratified combustion by collecting fresh air on the cylinder head side with respect to the residual exhaust gas on the side. Also, it is necessary to perform transverse scavenging when the load is high. Therefore, in order to perform the swirl stratification at the time of the low load and the transverse scavenging at the time of the high load by switching, two fresh air ports are provided facing the exhaust port, and one fresh air port or an upstream fresh air port is provided. A fresh air control valve that is opened / closed according to the operating state of the engine is arranged in the air passage. When the fresh air control valve is closed, fresh air is supplied from only one fresh air port to achieve swirl stratification. When the fresh air control valve is opened, fresh air is supplied from both fresh air ports, and in this case, fresh air flows in parallel from both fresh air ports, so swirl is not formed and cross scavenging is achieved. . A fresh air valve is arranged at each of these fresh air ports.

[Problems to be solved by the invention]

In a two-cycle internal combustion engine, exhaust gas remains in the combustion chamber because it is exhausted by scavenging as described above, and the ratio of fresh air supplied to the residual exhaust gas in the combustion chamber decreases in the idle and light load regions, resulting in combustion failure. There was a problem of becoming stable. In order to solve this, as described in the above-mentioned prior application, the exhaust gas discharged from the exhaust port at the time of opening the exhaust valve, especially at the time of idling or the operating condition with a small fresh air amount in the light load region. Part of the air is swirled around the cylinder axis and re-injected to form stratification of the fresh air and the residual exhaust gas, and a spark plug is formed in the rich mixture layer formed in the vicinity of the cylinder head. It is advantageous to be able to ignite easily by means of. Also, when the load is high, it is necessary to suppress swirl and perform transverse scavenging.
The present invention aims to provide a two-cycle internal combustion engine having a combustion chamber structure suitable for forming a swirl in the combustion chamber at a low load and performing transverse scavenging at a high load, and in particular, a transverse engine. The purpose is to prevent fresh air from directly blowing toward the exhaust valve when performing scavenging.

[Means for solving problems]

A two-cycle internal combustion engine according to the present invention is a fresh air supply system having a supercharging means and a fresh air driven in synchronization with a crank angle for opening and closing a fresh air port and an exhaust port provided in a cylinder head portion. In a two-cycle internal combustion engine having a valve and an exhaust valve, the exhaust port causes a part of the exhaust gas exhausted from the exhaust port when the exhaust valve is opened to re-inject into the combustion chamber while swirling around the cylinder axis. Is connected tangentially to each other, and two fresh air ports each having a fresh air valve are provided facing the exhaust port, and one fresh air port or a fresh air passage upstream thereof is opened and closed according to the engine operating state. The fresh air control valve is disposed, and the fresh air valve disposed in the fresh air port on which the fresh air control valve is disposed has a curvature of the neck portion more than that of the fresh air valve disposed in the other fresh air port. Large radius formed And it is characterized in that is.

[Action]

According to the present invention, stratification is achieved as follows in a low load region including at least idle. That is, if the exhaust valve opens during the downward stroke of the piston, a weak exhaust blowdown occurs and the exhaust port becomes positive pressure. The exhaust blowdown ends in a predetermined short time, and the piston continues to descend, so that the inside of the cylinder has a negative pressure with respect to the exhaust port, and part of the exhaust gas that has once been exhausted reflows into the combustion chamber. An exhaust port is tangentially connected to the combustion chamber to swirl this re-inflowing exhaust gas around the cylinder axis. Further, two fresh air ports each having a fresh air valve are provided facing the exhaust port, and one fresh air port or a fresh air passage upstream thereof is opened and closed according to the engine operating state. A valve is arranged and the fresh air control valve is closed at the time of the low load. On the other hand, when the load is high, the fresh air control valve is opened, and the amount of fresh air supplied is large, so the exhaust swirl is deenergized and cross scavenging is performed. The fresh air valve arranged on the fresh air port that is opened at the time of high load has a neck with a larger radius of curvature than the fresh air valve arranged on the other fresh air port. The flow of fresh air supplied from the fresh air port that is sometimes opened becomes a downward flow (toward the piston) so that it does not blow directly to the exhaust port.
The downward flow of fresh air makes a U-turn at the top surface of the piston and then returns to the upward direction, effectively replacing exhaust gas.

〔Example〕

First, description will be made with reference to FIGS. 2 to 4. 2 is a detailed view of the vicinity of the combustion chamber of one cylinder of FIG. 3, FIG. 3 is a view of a two-stroke internal combustion engine 10 of 6 cylinders to which the present invention is applied, and FIG. 4 is of FIG. It is a vertical sectional view which passes through a fresh air valve and an exhaust valve.

The engine body 10 is composed of a cylinder block 12 and a cylinder head 14, and a combustion chamber 18 is formed above the piston 16. Cylinder head 14 has fresh air port 20 and exhaust port
22 and 22 are formed so as to face each other, and each has a fresh air valve 24 and an exhaust valve 26 which are poppet valves.

As shown in FIG. 2, two fresh air valves 24 and two exhaust valves 26 are provided, and a spark plug 28 is provided substantially in the center of the combustion chamber 18. The exhaust valve 26 is represented by Es and E,
On the other hand, the fresh air valve 24 is represented by FA and FB. This is the fresh air valve 2
It is shown that the functions of 4 are different from each other.Hereafter, the fresh air valve represented by FA is called a low load fresh air valve, and the fresh air valve represented by FB is called a high load fresh air valve. To

As shown in FIGS. 2 and 3, the cylinder head 14
Two fresh air manifolds 30 and 32 are attached to the.
Each branch pipe of one fresh air manifold 30 is connected to the fresh air port 20 on the side where the low load fresh air valve FA is arranged, and each branch pipe of the other fresh air manifold 32 is arranged with the high load fresh air valve FB. Is connected to the fresh air port 20 on the operated side. Both fresh air ports 20 extend substantially parallel to each other in a direction substantially perpendicular to the longitudinal axis of the engine, and are on both sides of the center line of the cylinder in a direction substantially perpendicular to the longitudinal axis of the engine, and at least the low-load fresh air valve FA is arranged. The fresh air port 20 on the closed side opens tangentially to the combustion chamber 18. A fuel injection valve 34 is provided in each branch pipe of the fresh air port 20 or the fresh air manifolds 30, 32. Also, the fuel injection valve
A check valve 36 composed of a reed valve is arranged upstream of 34.

As shown in FIG. 3, the air is taken in from the air cleaner 38, the flow rate is controlled by the throttle valve 40, and the supercharger 42 is supercharged. An intercooler 44 is arranged downstream of the supercharger 42, and the two fresh air manifolds 30 and 32 are both connected to the intercooler 44. As the supercharger 42, a mechanical supercharger driven by the output of an engine such as a roots pump can be used. An air flow meter 46 is arranged upstream of the throttle valve 40.

A butterfly type fresh air control valve 48 is arranged at a gathering portion of the fresh air manifold 32 on the high load side. While the fresh air valve 24 and the exhaust valve 26 are driven by a cam shaft in synchronization with the crankshaft of the engine, the fresh air control valve 48 is opened and closed according to the load and the rotational speed of the engine. The fresh air control valve 48 is closed at low load, including at least when the engine is idle, and therefore, at this time, the air is fresh air on the low load side.
It will be supplied only from 30. The fresh air control valve 48 is opened at the time of high load in the engine, so that at this time, air is supplied through both the fresh air manifold 32 on the high load side and the fresh air manifold 30 on the low load side.

As shown in FIG. 3, two exhaust manifolds 50 are provided for the six cylinders, one exhaust manifold 50 is connected to the first, second, and third cylinders, and the other exhaust manifold 50 is the fourth, fifth, and fifth. , Connected to 6 cylinders. A catalyst 52 is arranged in a collection portion of each exhaust manifold 50, and each exhaust manifold 50 further terminates independently through each other through a muffler 54. In this case, the ignition order is the order of the first, sixth, second, fourth, third and fifth cylinders. Each exhaust manifold 50 has three branch pipes, and therefore one branch pipe is connected to the exhaust port 22 for one cylinder.

FIG. 2 shows one such branch pipe 50a,
0a is mounted almost at right angles to the longitudinal axis of the engine. By the way, each cylinder has two exhaust ports 22,
These two exhaust ports 22 are 1 inside the cylinder head 14.
Merged into one port. Exhaust valve indicated with Es 26
The exhaust port 22 in which the valve is arranged is formed substantially at right angles to the longitudinal axis of the engine so as to be aligned with the branch pipe 50a, and is tangentially connected to the combustion chamber 18. The other exhaust port 22 is joined at an angle to the exhaust port 22 on the side formed substantially at right angles to the longitudinal axis of the engine. The configuration of the exhaust port 22 is that the exhaust gas exhaust rate can be increased by having two exhaust valves 26, and the exhaust gas is exhausted to the exhaust port 22 and the exhaust manifold 50, a part of which is exhausted. When re-entering the combustion chamber 18, due to the effect of inertia flowing in a straight line, there is almost no re-entry from the exhaust port 22 on the angled side,
Exhaust port with exhaust valve 26 shown with Es
Mainly through 22, this re-injected exhaust gas is capable of forming a swirl S around the cylinder axis.

This swirl S is the clockwise direction as seen in FIG. The (Es side) exhaust port 22 forming the swirl S faces the fresh air port 20 having the high load side fresh air valve FB in a straight line, and the fresh air valve having the low load side fresh air valve FA. The port 20 and the port 20 face each other with a center line interposed therebetween. Therefore, when the load is low, the fresh air valve FA on the low load side
When the fresh air supplied from the fresh air port 20 having a swirl by itself produces the swirl, the swirl has the same clockwise direction as the swirl S of the re-inflow exhaust gas. Since the fresh air control valve 48 is closed at the time of low load, there is no fresh air flow from the fresh air port 20 on the high load side facing the exhaust port 22 forming the swirl S, and the swirl S of the re-inflow exhaust gas is blocked. There is nothing and thus the swirl S can be retained.

As shown in FIG. 2, a mask 56 is formed on the inner wall of the cylinder head 14, that is, the upper wall of the combustion chamber 18. The mask 56 is formed so as to cross the combustion chamber 18 substantially parallel to the longitudinal axis of the engine and to block between the fresh air valve 24 and the exhaust valve 26.
Most of the center of the mask 56 is formed by a plate-like ridge which can be turned at a sharp angle, and the side edges have a gentle inclination. The spark plug 28 comes to the fresh air valve 24 side. This mask 56 also helps to form the swirl S. That is, the re-injected exhaust gas from the exhaust valve (E) 26 is hardly present as described above, and even if there is an inflow, it is blocked by the mask 56. The re-injected exhaust gas from the exhaust valve Es tries to swirl by itself as described above, and further, if there is a flow toward the center of the combustion chamber 18 that moves off the swirl toward the fresh air valve 24, this also flows to the mask 56. Blocked. Therefore, the re-injected exhaust gas from the exhaust valve Es is masked.
Only through the gently sloping regions of the side edges of 56 will they increasingly flow along the combustion chamber 18 and the cylindrical surface of the cylinder. Further, when the load is high, the fresh air supplied from the two fresh air ports 20 in parallel hits the mask 56 and is directed downward, so that the fresh air is prevented from directly blowing through the exhaust port 22. Since the spark plug 28 is located on the fresh air valve 24 side, it is possible to contact a richer air-fuel mixture even when the load is low.

FIG. 1 is a sectional view taken along the line I--I of FIG. The fresh air valve (FA) 24 on the low load side and the fresh air valve (FB) 24 on the high load side are formed on substantially the same plane and have substantially the same size. Two
The two fresh air ports 20 are also formed almost in parallel. However, the radius of curvature of the neck of the fresh air valve 24 is formed to be different, and the fresh air valve (FB) on the high load side disposed on the fresh air port 20 on which the fresh air control valve 48 is disposed. The neck portion of 24 is formed with a radius of curvature RB, and the neck portion of the fresh air valve (FA) 24 on the low load side arranged in the other fresh air port 20 is formed with a radius of curvature RA. In this case, RB is larger than RA. This difference in the radius of curvature of the neck of the fresh air valve 24 for the same valve seat dimensions results in a difference in the direction of flow of fresh air supplied from the annular gap between the valve and the valve seat. The flow directions are respectively indicated by arrows, and the angles between the flow directions and the cylinder head wall surface or Θ _L , Θ _S are indicated. Θ _L is larger than Θ _S, and the fresh air supplied from the fresh air valve (FB) 24 on the high load side having the larger radius of curvature flows at a larger angle. The large angle in this case means that the angle is downward with respect to the wall surface of the cylinder head. Therefore, when only the fresh air valve (FA) 24 on the low load side is opened, fresh air is supplied at a more horizontal angle, which is more suitable for forming a swirl around the cylinder axis. When fresh air is supplied from the fresh air valve (FB) 24 on the high load side, it flows downward, so that it does not blow directly through the exhaust valve 26 and cooperates with the mask 56 to make a U-shape inside the cylinder. It is possible to traverse across the air.

Explaining the exhaust gas pressure here, when the engine load is low, there is a weak exhaust blowdown immediately after the exhaust valve 26 is opened and the exhaust port becomes a positive pressure, and the exhaust pressure of the combustion chamber 18 drops sharply. To do. When the pressure of the combustion chamber 18 becomes lower than the pressure of the exhaust port due to the downward movement of the piston 16, a part of the exhaust gas discharged from the combustion chamber by the exhaust blowdown is burned by the pressure difference between the exhaust port 22 and the combustion chamber 18. It comes to reflow (backflow) into the chamber 18.

Thus, when the engine load is low, there is a backflow of exhaust gas into the combustion chamber immediately after a weak exhaust blowdown. In the present invention, the exhaust gas that flows back into the combustion chamber is swirl S around the cylinder axis in the combustion chamber 18 as shown in FIG.
Are formed. Although it has been proposed in the past to generate swirl in the intake air sucked from the intake port, generating swirl in the backflowing exhaust gas is a major feature of the present invention.

Fig. 5 shows a fresh air valve driven in synchronization with the crankshaft
It is a figure showing a valve opening period (FO) of 24 and a valve opening period (FO) of an exhaust valve 26. In a two-cycle internal combustion engine, there are only two strokes, an expansion stroke in which the piston 16 descends from the top dead center TDC to the bottom dead center BDC and a compression stroke in which the piston 16 rises from the bottom dead center BDC to the top dead center TDC. And inhalation is at bottom dead center BD during these two strokes
It is performed near C, and basically, the fresh air pushed in by the supercharger 42 includes scavenging for exchanging gas while pushing out exhaust gas. Since there is a large amount of fresh air and fuel at high load, and therefore the amount of exhaust gas remaining in the cylinder is small, there are few combustion problems, but at idle and at low load, the amount of fresh air and fuel is small, and residual exhaust gas remains. Combustion must be performed in the presence of a large amount of gas, and when fresh air and exhaust gas are mixed, the air-fuel ratio becomes thin, making ignition combustion extremely difficult.

In the present invention, the exhaust valve 26 opens at 80 degrees before the bottom dead center BDC, and at this time, the piston 16 descends at a high speed, so that the pressure in the combustion chamber 18 does not change after the weak exhaust blowdown at idle and at low load. The back pressure of the exhaust port 22 and the negative pressure of the combustion chamber 18 ensure that a reverse flow of exhaust gas occurs. The exhaust valve 26 closes at 40 degrees after bottom dead center BDC. Further, the fresh air valve 24 opens at the time when exhaust gas reverse flow occurs after the exhaust valve 26 opens, for example, at 60 degrees before the bottom dead center BDC, and the bottom dead center after the exhaust valve 26 closes. Closes at 60 degrees after BDC.

FIG. 6 is a diagram for explaining backflow of exhaust gas and swirl generation at idle and at low load, and stratification of fresh air and residual exhaust gas generated thereby. At this time, the intake control valve 48 is closed and the fresh air is supplied by the low-load fresh air valve (F
A) Only from the 20 side. This supply of fresh air is slow because the wall itself is small and the boost pressure is low.
As shown in FIG. 6 (a), when the temperature reaches 80 degrees before the bottom dead center BDC, the exhaust valve 26 opens, and exhaust blowdown with a weak pressure P occurs. This exhaust blowdown is completed in a short time at idle and at low load. For example, exhaust port in weak exhaust blowdown at idle and low load
The pressure of 22 momentarily becomes about ² to 3 kg / cm ² , but immediately drops to about 1.05 kg / cm ² , and stabilizes while maintaining a positive back pressure.

As the piston 16 descends, negative pressure is generated in the combustion chamber 18,
As shown in FIG. 2B, the exhaust gas re-enters as shown by the arrow Q, and the swirl S of the exhaust gas is formed in the combustion chamber 18 by the structure of the exhaust port 22, the swirl forming means such as the mask 56. . At 60 degrees before bottom dead center BDC, the low-load fresh air valve (F
A) 20 opens. Fresh air is metered by the throttle valve 40, and the supercharging pressure of the supercharger 42 is also relatively low. In addition, since it takes time for the fresh air valve 24 to substantially fully open, fresh air does not immediately flow in, and exhaust gas backflow and swirl formation do not occur even when the low-load fresh air valve (FA20) is opened. in the process of. The formation of the exhaust swirl thus continues for a considerable time, which swirl forms around the cylinder axis.

Then, as shown in FIGS. 6 (c) and 6 (d),
Fresh air comes in when the fresh air valve 24 is practically fully opened. At this time, the descending speed of the piston 16 is also small, so that almost no negative pressure is formed in the combustion chamber and the supercharging pressure is small as described above.
to go into. Therefore, the inflowing fresh air slowly rides on the exhaust swirl and is supplied so as to rotate in the same direction as described above, and thus swirls together with the exhaust swirl on the exhaust swirl. In this way, the fresh air gathers at a portion of the cylinder head 14 side close to the spark plug 28 side, that is, the stratification of the fresh air on the cylinder head 14 side and the exhaust gas on the piston 16 side is achieved. The stratification of the fresh air and the exhaust is maintained even after the piston 16 descends to the bottom dead center, as shown in FIG. 6 (e). Even if the piston 16 goes up after passing through the bottom dead center, the movement speed is slow for a while, and the catalyst 52 provided in each exhaust manifold 50 is connected to the exhaust port.
22 and exhaust manifold 50 pressure drop can be prevented,
Outflow of fresh air from the combustion chamber 18 to the exhaust port 22, so-called blow-through of fresh air, hardly occurs. Further, it has been confirmed that the catalyst 52 provided in each exhaust manifold 50 has a function of reflecting the pressure at the time of exhaust blowdown, and this reflected pressure turned upward after the piston 16 passed the bottom dead center. Later, back pressure is applied to the combustion chamber 18 to effectively prevent fresh air from blowing through. Then, the fresh air valve 24 is closed and the fresh air supply to the cylinder is finished.

Fuel is injected at the appropriate time before the fresh air valve 24 closes. Therefore, at the time of idling and at the time of light load, the rich air-fuel mixture gathers at a portion of the cylinder head 14 side close to the spark plug 28 side, and is easily ignited by the spark plug 28 so that reliable combustion can be obtained. Then, this air-fuel mixture is placed on the exhaust gas, is activated by the high-temperature exhaust gas, forms an active heat atmosphere state containing radical fuel components, and burns in a state where ignitability is enhanced. You can do it.

When the load is medium or high, the fresh air control valve 48 is opened so that fresh air is supplied through both fresh air ports 24.
A large amount of air can pass through the fresh air port FB24 on the high load side. In this way, when the amount of fresh air increases, the swirl effect of the re-inflow exhaust gas disappears, and a large amount of fresh air is used for cross-scavenging. At this time, since there is the mask 56 that crosses the center of the cylinder head 14 and the radius of curvature of the neck portion of the fresh air valve 24 on the high load side is formed large, fresh air flows downward as described above. After all, fresh air first flows downward, then hits the piston 16 and then upwards, so that scavenging can be performed with a U-shaped flow.

[Effect of device]

As described above, according to the present invention, stratification can be achieved between fresh air and residual exhaust, especially at idle and low load, and transverse scavenging can be performed at high load, which is good from low load to high load. It is possible to obtain a two-cycle internal combustion engine that can perform various combustions.

[Brief description of drawings]

1 is a sectional view taken along the line I--I of FIG. 2, FIG. 2 is a view showing the vicinity of the combustion chamber of one cylinder of FIG. 3, and FIG. 3 is a two-cylinder 6 cylinder to which the present invention is applied. 4 shows a cycle internal combustion engine, FIG.
FIG. 5 is a vertical sectional view through the fresh air valve and the exhaust valve of FIG. 2, FIG. 5 is a diagram showing valve timing, and FIG. 6 is an explanatory diagram for explaining stratification at low load. 14 ... Cylinder head, 16 ... Piston, 18 ... Combustion chamber, 20 ...
Fresh air port, 22 ... Exhaust port, 24 ... Fresh air valve, 26 ... Exhaust valve, 42 ... Supercharger, 48 ... Fresh air control valve, 56 ... Mask.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Creator Toshio Ito 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Corporation (56) Reference JP-A-53-46516 (JP, A) JP-A-62-291427 (JP, A) JP 60-5770 (JP, B2)

Claims (1)

[Scope of utility model registration request] 1. A fresh air supply system having a supercharging means, and a fresh air valve and an exhaust valve driven in synchronization with a crank angle to open and close a fresh air port and an exhaust port provided in a cylinder head portion. In a two-cycle internal combustion engine having an exhaust port, the exhaust port is tangential to the combustion chamber to swirl a portion of the exhaust gas discharged from the exhaust port when the exhaust valve is opened into the combustion chamber while swirling around the cylinder axis. Two fresh air ports each having a fresh air valve connected thereto are provided so as to face the exhaust port, and one fresh air port or a fresh air passage upstream thereof is opened / closed in accordance with an engine operating state. The fresh air control valve is arranged, and the fresh air valve arranged in the fresh air port on which the fresh air control valve is arranged has a neck radius of curvature larger than that of the fresh air valve arranged in the other fresh air port. Being large Two-cycle internal combustion engine which is characterized.