JPH04203313A - Structure of combustion chamber in engine - Google Patents

Abstract

PURPOSE:To strengthen a swirl at the time when intake air flows in and strengthen an air flow in the vicinity of compression upper dead point by forming each mask part formed by downward swell of the inner wall face of a cylinder head around each cylinder periphery in the vicinity of the intake port opening part of a combustion chamber. CONSTITUTION:Two intake ports 6, 7 are opened to a combustion chamber in point symmetry positions while holding the center 0 of a cylinder between them. There are provided mask parts 16, 17 formed by downward swell of the inner wall of a cylinder head 2 around cylinder periphery in the vicinity of the opening parts of the intake ports 6, 7 of the combustion chamber. Consequently, decrease in fluid speed of intake air which flows in the combustion chamber from the respective intake ports 6, 7 in an air intake stroke is suppressed so as to strengthen a swirl, and turbulence of the air flow can be increased in the vicinity of the compression upper dead point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a combustion chamber structure for an engine in which two intake bows (-) are opened into the combustion chamber at points symmetrical positions across the center of the cylinder bore.

[Conventional technology]

2. Description of the Related Art Conventionally, engines have been known in which two intake ports are provided per cylinder in order to secure the intake port opening area and to generate swirl. - In the combustion chamber structure of this type of engine used for boat fishing, the openings of two intake ports are arranged side by side in the direction of the cylinder row, etc., but with this structure, air is taken from both intake ports. When the
The air flowing into the combustion blank from both intake ports tends to interfere with each other and weaken the swirl.

Therefore, in order to correct the above-mentioned tendency, JP-A No. 47-2476
As shown in Japanese Patent No. 5, there is a combustion chamber structure of an engine in which two intake bores i~ are opened into the combustion chamber at points symmetrical positions across the center of the cylinder bore.

According to this structure, even when air is taken from both intake ports, the swirling directions of the airflows flowing into the combustion chamber from each are the same, so the airflows do not interfere and weaken each other's swirl. Combustibility is improved compared to the general structure described above.

[Problem to be solved by the invention]

In the conventional structure in which the two intake ports are point-symmetrically arranged as described above, when air is taken from both intake ports, intake resistance is reduced and airflow interference is avoided. Since the port opening area of the intake ports is relatively large and the intake air expands as it flows from each intake port into the combustion chamber, the flow velocity of the intake air decreases, and the swirl weakens due to this decrease in flow velocity. In addition, the swirl gradually attenuates after intake, making it difficult to obtain a sufficiently strong airflow near compression top dead center, where combustion begins. Note that as a method of increasing the intake flow velocity to strengthen the swirl, it is possible to reduce the passage area of the intake port or the intake passage leading to the intake port, but this method has the drawback of increasing intake air flow resistance.

In view of these circumstances, the present invention has been developed to reduce intake air inflow resistance, assist swirl generation during intake air inflow to strengthen swirl, and further strengthen airflow near compression top dead center to significantly improve combustibility. The present invention provides an engine combustion chamber structure that can be improved.

[Means for Solving the Problems] The present invention provides a combustion chamber structure for an engine in which two intake ports open into the combustion chamber at point-symmetrical positions across the center of the cylinder bore. A mask portion in which the inner wall surface of the cylinder head bulges downward is formed at the peripheral edge of the cylinder.

Preferably, the mask portion has a shape that protrudes toward the center of the cylinder from a portion along the cylinder periphery when viewed from below.

In addition to the above configuration, a mask is provided that bulges downward from the intake port opening position in a portion located perpendicular to the intake inflow direction of the intake port and between the intake port opening and the exhaust port opening. A section may be formed in advance. In this case, it is preferable that the intake valve that opens and closes the intake port and the exhaust valve that opens and closes the exhaust port are provided so that the inclination angles of their respective valve shafts with respect to the cylinder bore center line are different from each other.

[Effect]

According to the above configuration, the mask portion formed on the peripheral edge of the cylinder near the intake port opening suppresses the spread of intake air when it flows into the combustion chamber from each intake port during the intake stroke, thereby reducing the flow velocity. The effect of increasing turbulence, which is effective for promoting combustion, can be obtained near compression top dead center.

Furthermore, in addition to the above-mentioned mask part on the cylinder periphery, if a mask part is also formed in the part between the intake and exhaust ports in the direction perpendicular to the intake air inflow direction, it is possible to enter the combustion chamber from each intake port during the intake stroke. The effect of increasing the flow rate of the incoming intake air is increased.

〔Example〕

Embodiments of the present invention will be described based on the drawings.

1 to 4 show a first embodiment of the present invention. In these figures, the engine is shown in cylinder block 1
and a cylinder head 2 provided above. A cylinder hole 3 is formed in the cylinder block 1, and a piston 4 is fitted into the cylinder hole 3 so as to be vertically slidable, and a combustion chamber 5 is formed above the piston 4. The inner wall surface of the cylinder head 2 constituting the upper end of the combustion chamber 5 has a pent-roof shape in which both sides are symmetrically inclined so that the center portion is depressed upward in the cross section shown in FIG.

Two intake ports 6.7 and two exhaust ports 8.9 formed in the cylinder head 2 open into the combustion chamber 5. As shown in FIG. 1, the intake port 6.7
open into the combustion chamber 5 at points symmetrical to each other with respect to the cylinder bore center O. In short, one intake port 6 extends from one side of the cylinder head 2 toward the combustion chamber 5, opens into the combustion chamber 5 at a position offset in a predetermined direction with respect to the cylinder bore center 0, and opens into the combustion chamber 5 at a position offset in a predetermined direction with respect to the cylinder bore center 0. 7 extends from the other side of the cylinder head 2 to the combustion chamber 5 side, and is located on the side opposite to the intake port 6 with respect to the cylinder bore center O.
It opens into the combustion chamber 5 at this position. Furthermore, both exhaust ports 8.9 open into the combustion chamber 5 on the sides of the intake port 6.7.

Therefore, the exhaust ports 8, 9 are also arranged symmetrically with respect to the cylinder bore center O, and each intake port 6.7 and each exhaust port 8.9 are arranged adjacent to each other.

An intake valve 1 opens and closes an opening to each combustion chamber 5 for each intake port 6.7 and each exhaust port 8.9.
1.12 and the exhaust valve (not shown) are in the cylinder head 2.
is equipped with. These intake valves 11, 12 and exhaust valves are operated by a valve mechanism (not shown). Incidentally, a spark plug (not shown) facing the combustion chamber 5 is also attached to the cylinder head 2, and the spark plug is arranged, for example, near the center 0 of the cylinder bore.

Further, in the vicinity of the openings of the intake ports 6 and 7 leading to the combustion chamber 5 and around the cylinder periphery, mask portions 16 and 17 are formed in which the inner wall surface of the cylinder head bulges downward. ing. In this embodiment, as shown with diagonal lines in FIG. 1, a mask portion 16 is provided on the cylinder peripheral side in the range between the opening of the intake port 6 and the exhaust port 8 located on the front side in the opening direction. Similarly, a mask portion 17 is formed on the cylinder peripheral side in the range between the opening of the intake port 7 and the exhaust port 9 located on the front side in the opening direction. When viewed in vertical cross section, these mask portions 16 and 17 bulge out from the vent roof-like inclined surface of the cylinder head 2 at the upper end of the combustion chamber 5 to a height position comparable to that of the mating surface with the cylinder block 1 (
(See Figures 2 to 4), when viewed from below, it has a shape that protrudes toward the center of the cylinder from the part along the cylinder periphery between the intake port 6.7 and the exhaust port 8.9. (See Figure 1).

According to the structure of this embodiment, the intake port 8 opens at a position offset from the cylinder bore center 0.
The intake air flowing into the combustion chamber 5 from , 9 swirls,
Since the two intake ports 8 and 9 are arranged point-symmetrically across the cylinder bore center ○, both intake ports 8,
Flows of intake air introduced into the combustion chamber 5 from each other do not interfere with each other and swirl in the same direction. In this way, a swirl is generated during the intake stroke, and at this time, the mask portion 16.17 formed at the cylinder periphery near the intake port h8.9 in the combustion chamber 5 has an effect of assisting the swirl generation. It will be done. In other words, compared to the case where there is no mask portion 16.17, the direction of the intake air flowing into the combustion chamber 5 from the intake ports 8 and 9 is regulated, and the spread of intake air toward the cylinder periphery is suppressed, so that the combustion The flow rate of the intake air within the chamber 5 is increased, thereby enhancing the swirl.

- Further, the mask portions 16, 17 cause a change in the airflow within the combustion chamber 5 near the compression top dead center, thereby providing a flow that is advantageous for promoting combustion. In other words, at the beginning of compression when the piston 4 is near the bottom dead center, a swirl occurs along the circumferential direction of the cylinder (dotted line arrow in Fig. 1).
When it rises to near the top dead center and approaches the mask part 16.17, the swirl changes in the direction along the inside of the mask part 16.17 (solid line arrow in Fig. 1), and the swirl radius increases. becomes smaller, and the kinetic energy of the swirl is converted into turbulence energy. Therefore, turbulence in the airflow increases at compression top dead center, which promotes combustion.

5 to 7 show a second embodiment of the invention. In this embodiment as well, there are two intake ports 6.7 in the combustion chamber 5.
The structure in which the two exhaust bows h8 and h9 are open and the intake bows h6 and h7 are arranged point-symmetrically with respect to the cylinder bore center ◯ is the same as in the first embodiment. Furthermore, it is similar to the first real male side in that the inner wall surface of the vent roof-shaped cylinder head has a mask portion in the vicinity of the intake port opening of the combustion chamber 5 and around the cylinder periphery, in which the inner wall surface of the cylinder head bulges downward. , a mask portion 26.27 is not only formed at the cylinder periphery on the front side in the intake air inflow direction with respect to the intake port 6.7, but also a narrow mask portion 26.27 is formed on the cylinder periphery on the swirl upstream side with respect to the intake port 6.7. Mask portions 26', 27=
is formed. When viewed from below, the width of the mask on the downstream side of the swirl is in the range from the mask part 26' to the mask part 26 with the intake port 6 in between, and in the range from the mask part 27 to the mask part 27 with the intake port 7 in between. (The amount of protrusion from the cylinder periphery toward the cylinder center) gradually becomes thicker.

Also in this embodiment, the mask portion 26°27.2
6= and 27- provide the effect of promoting swirl generation during the intake stroke and the effect of changing the airflow to reduce the swirl radius near the top dead center of the compression stroke to promote combustion.

8 and 9 show a third embodiment of the invention. In this embodiment as well, the combustion chamber 5 has two intake ports 6.
7 and two exhaust ports 8.9 are open, and both intake ports 6.7 are arranged point-symmetrically with respect to the cylinder bore center 0. This is similar to the second embodiment. Furthermore, mask portions 36, 37.
36-37', but in addition, there are portions located perpendicular to the intake inflow direction of the intake port and between the intake port opening and the exhaust port opening, that is, the intake port 6 and the exhaust port 9. Mask portions 38 and 39 are formed between the intake port 7 and the exhaust port 8 and bulge downward from the intake port opening position.

In particular, in the illustrated example, each intake port 6.7 and the valve seat surface of each exhaust port 8, 9 are arranged at different angles, creating a step between these surfaces. intake valve 31 that opens and closes -6, 7 and each exhaust port 8.9
Exhaust valves 33 that open and close are arranged at mutually different inclination angles. That is, the inclination angle α of the valve shaft of the intake valve 31 and the inclination angle β of the valve shaft of the exhaust valve 33 with respect to the cylinder bore center line are different from each other (for example, α<β), and correspondingly, the inclination angle The valve seat forming surfaces are also formed at different angles for the intake port 6.7 and the exhaust port 8.9, and between these valve seat forming surfaces, there is a recess so that the intake port side is recessed upwards than the exhaust port side as it approaches the cylinder periphery. It has a shape with a step.

Due to the stepped portion between the intake and exhaust ports, the mask portion 38, 39 bulges out below the intake port opening position.
is configured.

This structure also allows the mask portions 36, 37, 36-. 3
'M, 38.39 provides the effect of promoting swirl generation during the intake stroke and the effect of changing the airflow to reduce the swirl radius near the top dead center of the compression stroke and promote combustion. .

In particular, in addition to the mask part around the cylinder periphery, there is also a mask part 38.3 between the intake and exhaust ports in the direction perpendicular to the intake air inflow direction.
9 is provided, the effect of suppressing the spread of intake air and strengthening the swirl when intake air flows into the combustion chamber 5 is further enhanced.

〔Effect of the invention〕

As described above, according to the invention set forth in claim 1, the combustion chamber has two intake ports that open at points symmetrical positions across the center of the cylinder bore, and the intake ports are located near the openings of the respective intake ports and at the periphery of the cylinder. Since a mask part is formed in the part that bulges downward, it suppresses the decrease in the flow velocity of the intake air flowing into the combustion chamber from the above intake ports during the intake stroke, strengthens the swirl, and improves the swirl around the compression top dead center. The turbulence of the airflow is increased, and these effects can significantly improve combustibility.

In this configuration, when the mask portion has a shape that protrudes toward the cylinder center from a portion along the cylinder periphery when viewed from below, the swirl radius is reduced near the compression top dead center. This increases the turbulence of the airflow, making it possible to fully exhibit the above effects.

Furthermore, if a mask portion is also formed between the intake and exhaust ports in the direction perpendicular to the intake air inflow direction as described in claim 3,
The effect of strengthening the swirl during the intake stroke can be further enhanced. If the intake valve and the exhaust valve are provided so that the inclination angles of their respective valve shafts are different, the gap between the intake and exhaust ports is caused by the step created between the corresponding valve seat constituent surfaces. The mask portion can be formed simply and effectively.

[Brief explanation of the drawing]

FIG. 1 is a schematic bottom view of the combustion chamber forming portion of a cylinder head according to a first embodiment of the present invention, and FIG. 2 is a diagram showing ■-■ in FIG.
3 is a sectional view taken along the line ■-■ in FIG. 1, FIG. 4 is a sectional view taken along the IV-rV line in FIG. 1, and FIG. 5 is a combustion chamber formation of the cylinder head according to the second embodiment. Schematic bottom view of the part,
6 is a sectional view taken along the line Vl-Vl in FIG. 5, FIG. 7 is a sectional view taken along the line ■-vI in FIG. 5, and FIG. 8 is a schematic bottom view of the combustion chamber forming portion of the cylinder head according to the third embodiment. 9 is a sectional view taken along the line IX-IX in FIG. 8. 1... Cylinder block, 2... Cylinder head,
5... Combustion chamber, 6,7... Intake port, 16.17
゜26.26', 27.27=, 36.36', 37.
37-. 38.39...Mask section. "# Figure 8 Figure 9

Claims (1)

[Claims] 1. In an engine combustion chamber structure in which two intake ports are opened into the combustion chamber at points symmetrical positions across the center of the cylinder bore, the combustion chamber is located near the intake port opening of the combustion chamber and at the periphery of the cylinder. The combustion chamber structure of an engine is characterized in that the inner wall surface of the cylinder head is formed with a mask portion that bulges downward. 2. The engine combustion chamber structure according to claim 1, wherein the mask portion protrudes toward the center of the cylinder from a portion along the cylinder periphery when viewed from below. 3. A mask portion that bulges out below the intake port opening position is formed in a portion located in a direction perpendicular to the intake air inflow direction of the intake port and between the intake port opening and the exhaust port opening. The combustion chamber structure of an engine according to claim 1, characterized in that: 4. The combustion engine according to claim 3, wherein the intake valve that opens and closes the intake port and the exhaust valve that opens and closes the exhaust port are provided such that the inclination angles of their respective valve shafts with respect to the cylinder bore center line are different from each other. Chamber structure.