JPH0631146Y2 - Combustion chamber structure of two-cycle internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a combustion chamber structure of a two-cycle internal combustion engine.

[Conventional technology]

In a two-cycle diesel engine, there is known a two-cycle diesel engine in which an intake port and an exhaust port are extended upward in parallel with a cylinder axis in order to ensure good loop scavenging in a combustion chamber (for example, JP-A-52). -104613
Issue).

However, in this two-cycle engine, since the opening between the intake valve and the exhaust valve and the valve seat is open over the entire outer circumference into the combustion chamber, the fresh air that has flowed in from the intake valve opening located on the cylinder axis side is exhausted along the inner wall surface. Outflow through the valve.

As a result, good stratification due to diffusion of the air-fuel mixture cannot be obtained, and the air-fuel mixture cannot be reliably ignited by the spark plug. The problem was that the rate deteriorated.

In order to solve such a problem, the applicant of the present invention previously filed Japanese Patent Application No.
-288390, a mask wall extending from the inner wall surface of the cylinder head toward the combustion chamber is formed between the air supply valve and the exhaust valve, and the mask wall is located between the air supply valve peripheral portion and the valve seat located on the exhaust valve side. Close the opening of the intake valve for the full opening period of the air supply valve 2
A combustion chamber structure for a cycle internal combustion engine is proposed. As a result, loop scavenging with the highest scavenging efficiency occurs in the combustion chamber,
The injection fuel and fresh air were mixed, and good stratification became possible.

[Problems to be solved by the device]

Although an extremely good combustion state can be obtained by such a proposal, in the case of a general center plug system in which a spark plug (spark plug) is provided in the center above the inner wall surface of the cylinder head, the mask of the ridge is used during a light load operation with little injected fuel. It is difficult to completely prevent misfires and knocks because the air-fuel mixture tends to be biased toward the end of the combustion chamber on the air supply valve side even if the engine is blocked by a wall, and the air-fuel mixture does not easily approach the spark plug even during medium-load operation. Is.

In view of the above, the present invention provides a combustion chamber structure for a two-cycle internal combustion engine, which is capable of ensuring a better ignition and combustion in the combustion chamber in order to solve such a problem and prevent misfire and knock in the present invention. With the goal.

[Means for Solving the Problems]

In order to achieve the above object, the combustion chamber structure of the two-cycle internal combustion engine of the present invention is characterized in that the spark plug electrode is provided at least on the far side from the exhaust valve near the intake valve.

〔Example〕

 Hereinafter, the present invention will be described with reference to the drawings.

1 to 3 show an example in which the present invention is applied to an embodiment of the combustion chamber structure of the Japanese Patent Application No. 62-288390 previously proposed by the applicant of the present application.

First, the proposed combustion chamber structure will be described. 1 is a cylinder block, 2 is a reciprocating piston in the cylinder 1, 3 is a cylinder head fixed on the cylinder block 1, and 4 is an inner wall surface of the cylinder head 3. 3a and 3b respectively show combustion chambers formed between the top surface of the piston 2 and 3a. A concave groove 20 is formed on the inner wall surface 3a of the cylinder head.
An air supply valve 6 is arranged on the inner wall surface portion 3b of the cylinder head forming the bottom wall surface of 0. On the other hand, the cylinder head inner wall surface portion 3c excluding the concave groove 20 is substantially flat, and the exhaust valve 7 is arranged on this portion 3c. The cylinder head inner wall surface portion 3b and the cylinder head inner wall surface portion 3c are connected to each other via the peripheral wall 21 of the groove 20.

The concave groove peripheral wall 21 is arranged very close to the peripheral portion of the air supply valve 6 and extends in an arc shape along the peripheral portion of the air supply valve 6, and a fresh air guide wall located between the air supply valve 6. 21b and a fresh air guide wall 21c located between the peripheral wall of the cylinder head inner wall surface 3a and the air supply valve 6.

Each mask wall extends toward the combustion chamber 4 below the air supply valve 6 at the maximum opening position, so that the exhaust valve 7
The opening between the peripheral portion of the air supply valve 6 located on the side and the valve seat 9 is closed by the mask wall 21a over the entire opening period of the air supply valve 6.

The new guide walls 21b, 21c are located in substantially the same plane and extend substantially parallel to the line connecting the centers of both air supply valves 6.

The spark plug 8 is arranged on the cylinder head inner wall surface portion 3c so as to be located at the center of the cylinder head inner wall surface 3a by a so-called center plug method.

The opening formed between the air supply valve 6 and its valve seat 9 is the exhaust valve 7
Since approximately 1/3 of the opening located on the side is closed by the mask wall 21a, fresh air is supplied from the remaining approximately 2/3 of the opening located on the side opposite to the exhaust valve 7. .

In addition, the fresh air flowing in from the air supply valve is the fresh air guide walls 21b and 21c.
Is guided downward along the inner wall surface of the cylinder.

Therefore, when the air supply valve 6 is opened, most of the fresh air flows toward the top surface of the piston 2 along the inner wall surface of the cylinder, as shown by the arrow S in FIG. 2, and thus good loop scavenging is performed. Be seen.

Regarding the opening timing of the intake valve 6 and the exhaust valve 7, for example, the exhaust valve 7 is opened earlier than the intake valve 6, and the exhaust valve 7 is closed earlier than the intake valve 6, The injection period can be set after the intake valve 6 is opened and before the piston 2 reaches the bottom dead center.

Here, the scavenging / stratification action will be described in more detail. When the piston 2 descends and the exhaust valve 7 opens, the high-pressure burned gas in the combustion chamber 4 flows into the exhaust port 13,
After a while, the pressure in the exhaust port 13 becomes almost atmospheric pressure. Next, when the piston 2 further descends, the pressure inside the combustion chamber 4 becomes negative, and the burnt gas in the exhaust port 13 flows back into the combustion chamber 4. The lower the load operation, the lower the combustion pressure. Therefore, since the time from the opening of the exhaust valve 7 until the pressure in the exhaust port 13 becomes almost atmospheric pressure is short, the backflow of burnt gas is faster as the engine load becomes smaller. Happens in time. When the piston 2 further descends, the fuel flows into the combustion chamber 4 together with the fresh air from the air supply port 12, but the mask wall 21 is opened against the opening of the air supply valve 6.
Since a is provided, the fresh air and fuel flow downward along the cylinder inner wall surface below the air supply valve 6. Therefore, the burned gas in the combustion chamber 4 is gradually pushed by the fresh air and discharged into the exhaust port 13, and thus the loop scavenging is performed in the combustion chamber 4.

Further, as described above, a backflow of burnt gas occurs after the exhaust valve 7 is opened. However, when this backflow of burned gas causes a looped flow of burned gas in the direction opposite to the loop scavenging S, stratification is performed. As a result, it becomes difficult to perform good ignition and combustion.
However, since the backflowed burnt gas is dispersed and flows into the combustion chamber 4 from the entire periphery of the exhaust valve 7, a looped burnt gas flow in the opposite direction to the loop scavenging S does not occur.
Therefore, the air-fuel mixture is not disturbed by the backflow of the burnt gas, and good stratification can be secured.

However, even with a combustion chamber structure capable of producing such an excellent combustion state, due to its structure, exhaust gas and air supply are performed at the same time, so that the amount of residual burned gas is large compared to a four-cycle internal combustion engine and good ignition is achieved. In order to secure the above, it is absolutely necessary to collect more air-fuel mixture around the spark plug. However, the mask wall 21a that enables good loop scavenging tends to hinder the supply of the air-fuel mixture to the central spark plug 8 on the contrary, and for example, the amount of fresh air and the amount of injected fuel that are supplied at the time of low load operation are absolutely Since the amount is small, the air-fuel mixture easily gathers in the combustion chamber 4 in the immediate vicinity of the air supply valve 6 as shown in FIG. 4 (A). Therefore, it may be difficult to completely prevent misfire and knocking only with the center plug 8. In order to solve this problem, the air supply valve 6 according to the present invention is used.
By providing the spark plug 18 on the far side from the nearby exhaust valve 7, reliable ignition and combustion can be performed. On the other hand, during medium load operation, the amount of fresh air and the amount of injected fuel are larger than under low load, and the region where the air-fuel mixture is formed spreads to the upper center of the combustion chamber, and ignition is possible only with the spark plug 8 (Fig. 4 (B )). However, from the viewpoint of shortening the combustion time and positively preventing knocking, the spark plugs 8 and 18 can be preferably used together.
That is, for example, when the load is low, only the spark plug 18
It is possible to perform complete and ideal ignition and combustion by switching such that ignition is performed only by the spark plug 8 when the load is medium or high.

By the way, regarding the fuel injection, when the load is light and the amount of fuel at idle is small, as shown in FIG.
The fuel can be concentrated in the vicinity to further improve the ignitability. That is, most of the injected fuel is supplied from the fuel injection valve 17 by injecting a rigid fuel having a small divergence angle from a distance (FIG. 5 (A) or a vicinity (FIG. 5 (B)). The atomized fuel is diffused into the fresh air flowing toward the spark plug 18 by colliding and atomizing it on the rear surface of the hood and further injecting the fuel toward the region on the spark plug 18 side with respect to the axis of the air supply port 12. (FIG. 6) As a result, the air-fuel mixture can be reliably formed around the spark plug 18 and very good ignition,
Combustion can occur.

The present invention has been described above by applying it to a two-cycle internal combustion engine having a combustion chamber structure having the above-mentioned mask wall. However, the idea of the present invention is broadly applicable to other two-cycle internal combustion engines without being bound by such a structure. It is also possible to apply the same to the same effect.

The center plug 8 is not essential in the present invention,
Of course, it does not matter, but the essence of the present invention is the spark plug 1
8 is provided at a predetermined position.

[Effect of device]

As described above, in order to completely eliminate the difficulty of ignition associated with the mask wall in a two-cycle internal combustion engine having a combustion chamber structure with a mask wall that enables extremely good scavenging and stratification, according to the present invention, near the air supply valve By installing a spark plug on the side far from the exhaust valve, it is possible to satisfactorily secure safe and reliable ignition and combustion not only during low load operation where ignitability is not good, but also during medium load operation, and effective misfire and knocking. Can be prevented.

[Brief description of drawings]

FIG. 1 is a side sectional view of a two-cycle internal combustion engine, FIG. 2 is a view similar to FIG. 1 when the intake valve 6 and exhaust valve 7 are opened, and FIG. 3 is a view showing an inner wall surface of a cylinder head. FIG. 4 is a diagram for explaining combustion at low and medium loads, FIG. 5 is a diagram showing a fuel injection method, and FIG. 6 is a diagram showing a cylinder head inner wall surface at the time of fuel injection. 1 ... Cylinder block, 2 ... Piston, 3 ... Cylinder head, 4 ... Combustion chamber, 6 ... Air supply valve, 7 ... Exhaust valve, 12 ... Air supply port, 13 ... Exhaust port, 17 ...... Fuel injection valve.

Claims (1)

[Scope of utility model registration request] 1. A mask wall extending from an inner wall surface of a cylinder head toward a combustion chamber is formed between an intake valve and an exhaust valve, and the mask wall is located between an exhaust valve side and an air intake valve peripheral portion and a valve seat. In the combustion chamber structure of a two-cycle internal combustion engine in which the opening of the intake valve is closed over the full opening period of the intake valve, a spark plug electrode is provided at least on the far side from the exhaust valve near the intake valve. Internal combustion engine combustion chamber structure.