JPH0264221A - Two-cycle internal combustion engine - Google Patents

Abstract

PURPOSE:To make both dimension and shape of an air supply valve and an exhaust valve substantially the same by closing an opening between a valve seat and the peripheral part on the exhaust valve side of the air supply valve for the entire period of valve-opening of the air supply valve. CONSTITUTION:A peripheral wall 8 of a recessed groove 5a, which connects inwall parts 3b and 3c of a cylinder head, consists of a pair of mask-walls 8a, which are situated very near to the peripheral part of an air supply valve 6 and moreover extend in an arced shape along the peripheral part of the air supply valve 6, and a fresh-air guide wall 8b, which is situated around an air supply valve 6. At this time, the mask- wall 8a extends toward a combustion chamber 4 beyond the maximum outer diameter part of the air supply valve 6, which is situated at the maximum left position of the valve 6. Accordingly, an opening between a valve seat 9 and the peripheral part on an exhaust valve (7) side of the air supply valve 6, is closed by the mask-wall 8a for the entire period of valve-opening of the air supply valve 6. With this contrivance, since the value-diameter of the exhaust valve 7 can be made larger, both dimension and shape of the air supply valve 6 and the exhaust valve 7 can substantially be made the same. As a result, the maximum number of revolutions of an engine can be increased.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a two-stroke internal combustion engine.

[Conventional technology]

A two-cycle engine that is equipped with an intake valve and an exhaust valve, and has a mask wall formed on the inner wall surface of the cylinder head to close the opening between the intake valve periphery and the valve seat on the exhaust valve side during the full opening period of the intake valve. internal combustion engine, )<already proposed by the applicant (
(See Japanese Patent Application No. 102659/1983).

In this two-stroke internal combustion engine, by providing a mask wall to the air intake valve, fresh air supplied from the air intake port does not blow through into the exhaust boat, and most of the fresh air flows through the mask wall. The air flows into the combustion chamber from the intake valve opening on the opposite side and flows in a loop within the combustion chamber, thus ensuring a good scavenging effect.

[Problem to be solved by the invention]

By the way, in an internal combustion engine in which a camshaft drives the intake and exhaust valves that are biased in the closing direction by a valve spring, the intake and exhaust valves tend to separate from the cams as the engine speed increases. In order to prevent this, it is necessary to set a large spring load on the valve spring.In other words, the higher the maximum engine speed, the greater the spring load on the valve spring.Also, the weight of the intake and exhaust valves increases. However, there is a limit to the spring load of the valve spring in view of the durability of the valve spring, and therefore, as the weight of the intake and exhaust valve increases, the engine's maximum rotation speed, that is, the permissible engine speed, increases. You will have no choice but to set the rotation speed low.

In this case, if the intake valve and exhaust valve have different weights, the allowable rotation speed j is determined by the heavier valve.

There is a limit to the space available for mounting the intake valve and the exhaust valve on the inner wall surface of the cylinder head, so if the diameter of one valve is increased, the diameter of the other valve must be decreased. In this case, the allowable rotational speed is determined by the weight and large diameter of the valve, so to maximize the allowable rotational speed, the valve diameters, that is, the weights of the intake and exhaust valves should be made substantially the same. Is required. However, in the two-stroke internal combustion engine mentioned above, the diameter of the intake valve is larger than the diameter of the exhaust valve, that is, the weight of the intake valve is heavier than the weight of the exhaust valve, and thus the permissible engine speed is low. There is a problem in that the engine speed cannot be increased because of this.

In addition, in order to reduce the amount of residual burnt gas in a two-stroke internal combustion engine, it is necessary to generate a strong blowdown when the exhaust valve opens. The diameter of the exhaust valve must be increased. However, in the above-mentioned two-stroke internal combustion engine, the diameter of the exhaust valve is smaller than the diameter of the intake valve, so it is difficult to generate a strong blowdown, so there is a problem that good scavenging action cannot be obtained. be.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a two-stroke internal combustion engine equipped with an air intake valve and an exhaust valve. A mask means is provided for closing the opening of the air supply valve and the air supply valve and the exhaust valve are substantially identical in size and shape.

[For production]

By making the intake and exhaust valves substantially identical in size and shape, the weights of the intake and exhaust valves are substantially equal, thus increasing the permissible rotational speed of the engine. Further, by making the intake valve and the exhaust valve substantially the same in size and shape, the diameter of the exhaust valve can be increased, thus providing a strong blowdown.

〔Example〕

Referring to FIGS. 1 and 2, 1 is a cylinder block, 2 is a piston that reciprocates within the cylinder block l,
Reference numeral 3 indicates a cylinder head fixed on the cylinder block l, and reference numeral 4 indicates a combustion chamber formed between the inner wall surface 3a of the cylinder head 3 and the top surface of the piston 2. A pair of concave grooves 5. a and 5b are formed, and the groove 5a is formed deeper than the groove 5b as a whole.

Cylinder head inner wall surface portion 3b forming the bottom wall surface of the groove 5a
A pair of air supply valves 6 are arranged above, and a pair of exhaust valves 7 are arranged on the cylinder head inner wall surface portion 3c forming the bottom wall surface of the groove 5b. These air supply valve 6 and exhaust valve 7 are driven by a cam (not shown). The angle of inclination of the cylinder head inner wall surface portion 3b and the angle of inclination of the cylinder head inner wall surface portion 3C are equal, and therefore the angle of inclination of the valve shaft of the intake valve 6 and the angle of inclination of the valve shaft of the exhaust valve 7 are also equal. Further, the dimensions and shapes of each intake valve 6 and each exhaust valve 7 are substantially equal, and therefore the weight and valve diameter of each intake valve 6 and each exhaust valve 7 are substantially equal. Further, as can be seen from FIG. 2, each intake valve 6 and each exhaust valve 7 are arranged point-symmetrically with respect to the cylinder axis at an angular interval of 90 degrees.

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 8 of the groove 5a. This concave groove peripheral wall 8 is arranged very close to the peripheral edge of the air supply valve 6 and extends in an arc shape along the peripheral edge of the air supply valve 6. and a guide wall 8b. Furthermore, a pair of fresh air guide walls 8C extending from the peripheral edge of the intake valve 6 to the peripheral edge of the cylinder head inner wall surface 3a are formed on the cylinder head inner wall surface 3a, and these fresh air guide walls 8C are formed on the cylinder head inner wall surface 3a. It extends from the portion 3b to the cylinder head bottom wall surface portion 3d. Each mask wall 8a has a corresponding fresh air guide wall 8C
connected to. Each mask wall 8a extends toward the combustion chamber 4 below the maximum outer diameter of the intake valve 6 at the maximum lift position shown by line Ii in FIG. The opening between the peripheral edge of the air supply valve 6 and the valve seat 9 is closed by the mask wall 8a throughout the opening period of the air supply valve 6. Further, the fresh air guide walls 13b, 8c are located on substantially the same plane, and furthermore, these fresh air guide walls 8b, 8c extend substantially parallel to the line connecting the centers of both air supply valves 6. There is.

The ignition plug IO is arranged on the inner portion 3C of the cylinder head inner wall so as to be located at the center of the cylinder head inner wall surface 3a. On the other hand, the exhaust valve 7 is not provided with a mask wall that covers the opening between the exhaust valve 7 and the valve seat 11. Therefore, when the exhaust valve 7 opens, a mask wall is formed between the exhaust valve 7 and the valve seat 11. The entire opening opens into the combustion chamber 4.

Inside the cylinder head 3, an air supply boat 1 is provided for an air supply valve 6.
2 is formed, and an exhaust port 13 is formed for the exhaust valve 7. Each air supply boat 12 is connected to an air cleaner (not shown) via a mechanical supercharger (not shown) driven by an engine, for example.
(not shown). A fuel injection valve (not shown) is disposed within each air supply boat 12 or within the combustion chamber 4, and fuel is injected into the air supply boat 12 or the combustion chamber 4 from this fuel injection valve.

FIG. 3 shows an example of the opening period of the intake valve 6 and the exhaust valve 7. In the example shown in FIG. 3, the exhaust valve 7 opens before the intake valve 6, and the exhaust valve 7 closes before the intake valve 6. Furthermore, the valve lift curve of the intake valve 6 is substantially equal to the valve lift curve of the exhaust valve 7, and therefore the maximum lift amounts of the intake valve 6 and the exhaust valve 7 are substantially equal.

Figure 4 shows the valve lifts of the intake valve 6 and exhaust valve 7 and pressure changes in the exhaust port 13 P+, PzQ+, Qt.
It shows. These pressure changes P1゜PK, Q+
, Qz will be described later.

Next, the scavenging action and stratification action will be explained with reference to FIGS. 5 and 6. FIG. 5 shows the state of low load operation, and FIG. 6 shows the state of high load operation. 5(A) and 6(A) show the state immediately after the air supply valve 6 is opened, and FIG. 5(I3) and FIG. 6(B) show the piston 2 almost at the dead center. It shows when it is.

First, with reference to FIG. 5, the operation during low engine load operation will be described.

When the piston 2 descends and the exhaust valve 7 opens, the high-pressure burnt gas in the combustion chamber 4 suddenly blows down into the exhaust port 13, resulting in exhaust gas as shown by P in FIG. The pressure within the port 13 temporarily becomes positive. This positive pressure P propagates downstream in the exhaust passage, is reflected at the gathering part of the exhaust passages of each cylinder, and becomes negative pressure and propagates into the exhaust port 13 again. Therefore, when the air supply valve 6 opens, negative pressure is generated within the exhaust port 13, as indicated by P2 in FIG. The timing at which negative pressure is generated depends on the length of the exhaust passage. During low load operation of Ia, the combustion pressure is low, and therefore the positive pressure PI and negative pressure P2 generated in the exhaust port 13 are relatively small.

When fuel is injected into the air supply boat 12, when the air supply valve 6 opens, fresh air containing fuel flows from the air supply boat 12 into the combustion chamber 4, but the opening of the air supply valve 6 On the other hand, since the mask wall 8a is provided, fresh air and fuel mainly flow into the combustion chamber 4 through the opening of the intake valve 6 on the opposite side to the mask wall 8a. On the other hand, when the intake valve 6 opens, negative pressure is generated in the exhaust port 13 as shown by P2 in FIG. Due to the movement of this burnt gas sucked in, fresh air and fuel are drawn toward the exhaust valve 7 as shown by arrow R1 in FIG. 5(A),
Fuel is thus directed around the spark plug 10 (FIG. 2). Next, as shown in FIG. 5(B), when the piston 2 descends, the fresh air containing fuel moves downward along the inner wall surface of the cylinder below the intake valve 6, as shown by Ri.

However, when the engine is operating at low load, the amount of fresh air flowing into the combustion chamber 4 is small and the speed of the fresh air flowing into the combustion chamber 4 is slow, so that the fresh air does not reach the top surface of the piston 2 and remains in the upper part of the combustion chamber 4. Therefore, when the piston 2 rises, the air-fuel mixture gathers in the upper part of the combustion chamber 4, and residual burnt gas gathers in the lower part of the combustion chamber 4, so that the inside of the combustion chamber 4 becomes stratified. In this way, the air-fuel mixture is reliably ignited by the ignition plug 10.

On the other hand, when the engine is operated under high load, the combustion pressure increases, so the positive pressure generated in the exhaust port 13 increases as shown by 01 in FIG. 4, and the negative pressure Q which is the reflected wave of this positive pressure Q1 : also gets bigger.

Further, the peak of the negative pressure Q occurs slightly later than the peak of the negative pressure P.

When the engine is operated under high load, the amount of fresh air flowing into the combustion chamber 4 is large, and the speed of the air flowing into the combustion chamber 4 is high. Therefore, when the intake valve 6 opens, a large amount of fresh air flows into the combustion chamber 4 at high speed.
Next, when the burnt gas in the upper part of the combustion chamber 4 is sucked out into the exhaust port 13 by the negative pressure Q generated in the exhaust port 13, new gas is generated as shown by arrows S+ and St in FIG. 6(A). The air is directed towards the center of the combustion chamber 4.

Then, when the piston 2 further descends, the fresh air heads downward along the inner wall surface of the cylinder below the air supply valve 6 and reaches the top surface of the piston 2, as shown at 52 in FIG. 6(B). Therefore, the burnt gas in the combustion chamber 4 is gradually driven away by fresh air and discharged into the exhaust port 1-13 as shown by the arrow T in FIG. Scavenging will be carried out.

Furthermore, in the embodiment shown in FIGS. 1 and 2, since each fresh air guide wall 9b, gc is provided, each air supply port 1
A part of the fresh air supplied from 2 is shown by arrow S4 in Fig. 6(B).
As shown, the fresh air is guided by the respective guide walls 8b and 8c and reaches the vicinity of the top surface of the piston 2, so that the fresh air flow S4 also scavenges the air in the combustion chamber 4.

Another embodiment is shown in FIGS. 7 and 8. In this embodiment, the same components as in FIGS. 1 and 2 are designated by the same reference numerals.

Referring to FIGS. 7 and 8, the dimensions and shapes of each intake valve 6 and each exhaust valve 7 are substantially the same in this embodiment, and therefore the weight of each intake valve 6 and each exhaust valve 7 is The diameters are substantially equal. On the other hand, in this embodiment, the mask wall 8 as shown in FIGS.
a is not provided, and instead of the mask wall 8a, a shroud 2o extending in an arc shape along the peripheral edge of the seven exhaust valves is attached to the back surface of the bulk part of each air supply valve 6. As a result, the opening between the peripheral edge of the air supply valve 6 located on the exhaust valve 7 side and the valve seat 9 is closed during the full opening period of the air supply valve 6. Therefore, when the intake valve 6 opens, fresh air flows into the combustion chamber 4 from the opening of the intake valve 6 on the opposite side of the shroud 20 as shown by the arrow U in FIG. 9, thus creating a good loop. Scavenging is performed.

As described above, in each embodiment, each air intake valve 6 and each exhaust valve 7 are formed to have substantially the same weight. Therefore, the permissible engine speed becomes higher, so that the maximum engine speed can be increased. Further, in any of the embodiments, the valve diameters of each intake valve 6 and each exhaust valve 7 are formed to be substantially equal. In other words, the exhaust valve 7 has a large valve diameter. As a result, the opening surface of the exhaust valve 7 becomes larger when the exhaust valve 7 opens, so that the burned gas in the combustion chamber 4 easily flows out into the exhaust port 13, thus causing a strong blowdown. is obtained, as a result,
As the amount of burned gas fireflies in the combustion chamber 4 decreases, the pressure in the combustion chamber 4 rapidly decreases, making it easier for fresh air to flow into the combustion chamber 4, thus increasing the scavenging efficiency.

Although the present invention has been described so far in the case where it is applied to a two-stroke gasoline engine, the present invention can also be applied to a two-stroke diesel engine.

〔Effect of the invention〕

Since the maximum rotational speed of the engine can be increased, the engine output can be increased, and since a good scavenging action can be ensured, the engine output can be further increased.

[Brief explanation of the drawing]

Figure 1 is a side sectional view of a two-stroke internal combustion engine, Figure 2 is a diagram showing the inner wall surface of the cylinder head, Figure 3 is a diagram showing the opening period of the supply and exhaust valves, and Figure 4 is the valve of the supply and exhaust valves. A diagram showing the pressure changes inside the lift and exhaust boat, Figure 5 is a diagram to explain the operation during low load operation, Figure 6 is a diagram to explain the operation during high load operation, and Figure 7 is a diagram to explain the operation during high load operation. FIG. 8 is a side sectional view of a two-stroke internal combustion engine showing another embodiment, FIG. 8 is a view showing the inner wall surface of the cylinder head of FIG. 7, and FIG. 9 is a view for explaining the operation. 3... Cylinder head, 4... Combustion chamber, 6...
- Air supply valve, 7... Exhaust valve, 8a... Mask wall, 3b, 3c... Fresh air guide wall, 12... Air supply boat, 20... Shroud. Figure Figure 12... Air supply boat (A) (A) (B) Figure 7

Claims (1)

[Claims] In a two-stroke internal combustion engine equipped with an air intake valve and an exhaust valve, a mask means is provided for closing an opening between the air intake valve periphery and the valve seat on the exhaust valve side during the full opening period of the air intake valve. and a two-stroke internal combustion engine with exhaust valves having substantially the same size and shape.