JP3109654B2 - Combustion chamber of two-stroke water-cooled engine for motorcycles - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-stroke water-cooled engine for a motorcycle, and more particularly to a structure of a combustion chamber thereof. 2. Description of the Related Art Conventionally, in a combustion chamber of a two-stroke water-cooled engine, a dome located on the center line of a cylinder, as disclosed in Japanese Patent Application Laid-Open No. 51-29622, for example,
A ring-shaped squish zone spreading continuously toward the outer circumference of the piston top surface is provided continuously, and when the piston reaches near top dead center, the air-fuel mixture is compressed by the squish zone and ejected into the dome In such a case, the ignition ratio and the flame propagation speed are increased by concentrating the air-fuel mixture in the dome, and the output is promoted. [0003] However, when such a flame propagation speed is increased, the pressure in the cylinder is rapidly increased, so that an impact particularly applied to the piston top surface is increased. Therefore, not only was the top surface of the piston struck, but the vibration of the piston was transmitted to the cylinder and the crankcase, which resonated and produced unpleasant resonance noise. . As a countermeasure against this, conventionally, a dome which is inclined inward toward the spark plug side has a long inclined surface, so that the distance from the ignition point to the squish zone is increased to propagate the flame in the combustion chamber. There is an example in which the speed is reduced and the pressure in the cylinder is gradually increased. However, according to the structure of the prior art, since the dome is deepened, when the piston reaches the top dead center, the mixing compressed by the squish zone is performed. The air does not sufficiently reach the vicinity of the spark plug. Therefore, although the noise is reduced, the original squish effect is impaired, and disadvantages such as a decrease in high output are caused. The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to reduce the impact applied to the piston top surface without lowering the output. It is an object of the present invention to provide a combustion chamber of a two-stroke water-cooled engine for a motorcycle that can reduce noise. SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a nozzle which is coaxially located on the center line of a cylinder and has a circular cross section along the radial direction of the cylinder. And the dome and the opening of the dome continue to spread toward the outer periphery of the piston top surface. When the piston reaches the vicinity of top dead center, the air-fuel mixture is compressed and ejected into the dome. A ring-shaped squish zone to be provided, a spark plug is provided coaxially at the center of the top of the dome, and the inner peripheral wall of the dome is inclined radially inward as it goes toward the spark plug, It is assumed that the combustion chamber of a two-stroke water-cooled motorcycle engine has a combustion chamber in which the inclined surface is formed linearly along the axis of the dome. The top surface of the piston is formed in a curved convex shape, and the diameter of the tip surface of the dome is formed to be substantially the same as the diameter of the screw portion of the spark plug to form the curved surface of the dome tip.
The area of a surface concentric with the dome surrounded by the intersection of the extension line along the inclined surface of the dome and the plane passing through the maximum diameter portion of the squish zone, continuous with the screw portion of the spark plug Where S 1 is the area of a ring-shaped surface obtained by subtracting the area S 1 from the area of the plane passing through the maximum diameter portion of the squish zone, and S 2 / S 1> 1.4. Is what you do. FIG. 1 to FIG. 7 show an embodiment of the present invention. 5 and 6, reference numeral 1 denotes a cylinder block, 2 denotes a cylinder head, and a cylinder 1a is formed in the cylinder block 1. Cylinder 1
An intake port 4, an exhaust port 5, and a scavenging port 6 which are opened and closed by a piston 3 are opened on the inner peripheral surface of the cylinder a. Are in communication. A piston 3 is provided on the top of the cylinder 1a.
When the piston reaches the vicinity of the top dead center, a combustion chamber 9 is formed between the convexly protruding top surface 3 a of the piston 3 and the facing surface 2 a of the cylinder head 2. The combustion chamber 9 is provided with a center line O1 of the cylinder 1a.
And a dome 10 having a circular cross section along the radial direction of the cylinder 1a and located on the outer side of the top surface 3a of the piston 3 continuous with the opening of the dome 10. And a ring-shaped squish zone 11 that spreads out, and the top surface 3a of the piston 3 in the squish zone 11
Is inclined in a direction away from the top surface 3a as it proceeds radially inward. Therefore, in the compression stroke, when the piston 3 rises to the vicinity of the top dead center, the air-fuel mixture compressed by the squish zone 11 blows out into the dome 10 and the flow of the air-fuel mixture in the dome 10 is reduced. Promoted. The dome 10 and the squish zone 11
A step portion 14 is formed continuously in the circumferential direction at the boundary portion between. An ignition plug 12 is coaxially screwed into a front end face 10a of the dome 10.
The diameter L1 of a is substantially equal to the diameter of the screw portion 13 of the ignition plug 12. The inner peripheral surface of the dome 10 forms an inclined surface 10b which is inclined inward in the radial direction toward the spark plug 12 side.
a and the squish zone 11 are connected by smooth curved surfaces 10c, 10c,
0b, there is a fixed length h between the curved surfaces 10c, 10c.
A straight portion 10d along the axial direction of the dome 10 is formed over the dome 10. Therefore, the curved surface of the tip of the dome 10
10c is connected to the screw portion 13 of the ignition plug 12
become. In the combustion chamber 9 having such a configuration, FIG.
As shown in FIG. 5, the area of a surface concentric with the dome 10 surrounded by the intersection of the extension line along the inclined surface 10b of the dome 10 and the plane passing through the maximum diameter portion of the squish zone 11 is defined as When the area of the ring-shaped surface obtained by subtracting the area S1 from the area of the maximum diameter (bore diameter) of S1 and the squish zone 11 is defined as S2, the relationship is defined as S1 <S2. The cylinder block 1 and the cylinder head 2 are provided with a water jacket 16 surrounding the cylinder 1a and the combustion chamber 9. The water jacket 16 allows engine cooling water to flow therethrough. It has become. By the way, the present inventor has found that the inner diameter × the stroke is 56 ×
In a 50 mm two-cycle single-cylinder water-cooled engine, an experiment was conducted in which the area ratio S2 / S1 between the areas S1 and S2 was changed to measure the engine noise in each case. In this experiment, the noise measurement position was set at 50
mm. FIG. 3 shows the results of the experiment.
It was found that the relationship of 1 <S2 was satisfied, that is, the engine noise sharply decreased from the conventional level when the area ratio exceeded 1.4. That is, the reason for this is that if the relationship between the areas S1 and S2 is defined as S2 / S1> 1.4 as described above, the squish zone 11 becomes wider than the dome 10 and the squish effect is increased. As the amount of the air-fuel mixture burning rapidly in the dome 10 is substantially reduced, the flame that has grown in the dome 10 in combination with the presence of the step 14
Squish zone 1 that is harder to burn than inside this dome 10
It is considered that it takes time to propagate the gas into the combustion chamber 1 and the flame propagation speed in the combustion chamber 9 becomes slow. Thus, when the flame propagation speed becomes slow,
The pressure rise in the cylinder 1a with respect to the crank angle becomes gentle, and the impact applied to the top surface 3a of the piston 3 can be reduced. Moreover, if the area S1 is small, the piston 3
Is applied in a narrow range at the center of the top surface 3a, so that the vibration of the piston 3 is suppressed in conjunction with the reduction of the impact. Therefore, resonance of the cylinder block 1 and the crankcase 8 can be prevented, and noise from around the engine can be suppressed. On the other hand, when the present inventor examined the change of the cylinder internal pressure with respect to the crank angle when the combustion chamber 9 was formed as described above, the result shown in FIG. 4 was obtained. As is clear from FIG. 4, the time when the internal pressure becomes maximum slightly shifts to the bottom dead center side as compared with the conventional case indicated by the broken line, but there is hardly any difference in the change in the cylinder internal pressure. That is, the reason for this is that when the inside of the dome 10 becomes narrower and the piston 3 reaches the top dead center, the air-fuel mixture compressed in the squish zone 11 is drowned.
It is considered that the squish effect is sufficiently exerted over every corner in the system 10. Therefore, even if the flame propagation speed is low, the ignition rate is high and the flame is smoothly propagated to the air-fuel mixture at the end in the squish zone 11, so that the cylinder internal pressure rises to the same value as before, and the high Output in the rotation range can be secured at the same time. The top surface 3a of the piston 3 forming the bottom of the combustion chamber 9 is curved and convex, so that the combustion chamber 9
The squish effect inside the dome 10 is remarkably improved, and the diameter L1 of the tip surface 10a of the dome 10 is made substantially the same as the diameter of the screw portion 13 of the spark plug 12, and the tip curved surface 10c of the dome 10 is connected
The connection to the threaded portion 13 of the lug 12 facilitates ignition very easily and improves the ignitability. According to the present invention described in detail above, the flame propagation speed in the combustion chamber is reduced, and the pressure in the cylinder is gradually increased, so that the impact applied to the piston top surface is reduced. Noise from around the engine can be kept low. Moreover, when the piston reaches the top dead center, the air-fuel mixture compressed by the squish zone spreads to all corners of the dome, so that the original squish effect is sufficiently exhibited, and the Output can be secured at the same time. Then, the top surface of the piston is formed in a curved convex shape, and
The diameter of the tip of the dome is almost the same as the diameter of the screw of the spark plug, and the curved surface of the dome is connected to the screw of the spark plug.
Thus , the combustion chamber of the two-stroke water-cooled engine for a motorcycle can be significantly improved in squish effect and ignitability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing a sectional shape of a combustion chamber. FIG. 2 is an arrow view as viewed from a direction of a line II in FIG. 1; FIG. 3 is a noise characteristic diagram. FIG. 4 is a cylinder pressure characteristic diagram. FIG. 5 is a sectional view of a two-cycle water-cooled engine for a motorcycle. FIG. 6 is a sectional view taken along the line VI-VI in FIG. FIG. 7 is a bottom view of the cylinder head. [Description of Signs] 1a Cylinder 2 Cylinder head 3 Piston 3a Top surface 9 Combustion chamber 10 Dome 10b Inclined surface 11 Squish zone 12 Spark plug 13 Screw part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02P 13/00 302 F02P 13/00 302Z

Claims (1)

(57) [Claims] While being coaxially located on the center line of the cylinder,
A dome with a circular cross section along the radial direction of this cylinder, and a dome that is continuous with the opening of the dome toward the outer peripheral side of the piston top surface when the piston reaches near the top dead center. A ring-shaped squish zone for compressing the air-fuel mixture and ejecting the mixture into the dome. A spark plug is provided coaxially at the center of the top of the dome,
A two-stroke water-cooling system for motorcycles having a combustion chamber in which the inner peripheral wall of the dome is inclined radially inward toward the spark plug side and the inclined surface is formed linearly along the axial direction of the dome. In the combustion chamber of the engine, the top surface of the piston is formed in a curved convex shape, and the diameter of the tip surface of the dome is formed to be substantially the same as the diameter of the screw portion of the spark plug, thereby forming the curved surface of the dome tip. To the thread of the spark plug
Is continuous, the de - beam inclined surface along the extension line and Sukisshuzo - the de enclosed by intersection of the plane through the largest diameter portion of the down - arm concentrically with the area of the surface of S1, which forms the said Sukisshuzo - Two-cycle for a motorcycle characterized by the relationship of S2 / S1> 1.4 when the area S2 of the ring-shaped surface is obtained by subtracting the area S1 from the area of the plane passing through the maximum diameter portion of the motorcycle. The combustion chamber of a water-cooled engine.