JP2769811B2 - Two-cycle 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 and a cylinder thereof. 2. Description of the Related Art In a combustion chamber of a two-stroke chilled water engine, conventionally,
For example, as shown in JP-A-51-29622, a ring-shaped squish zone extending toward the outer peripheral side of the piston top surface is continuously provided on the dome located on the cylinder center line, and the piston is at the top dead center. When it reaches the vicinity, the air-fuel mixture is compressed in the squish zone and ejected into the dome, and the air-fuel mixture is concentrated in the dome, thereby increasing the ignition rate and flame propagation speed, and pushing for higher output. ing. 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 is the top surface of the piston struck, but the vibration of the piston is transmitted to the cylinder and the crankcase, which resonates to generate unpleasant resonance noise. As a countermeasure for this, conventionally, the inwardly inclined dome is formed with a longer slope toward the spark plug side to increase the distance from the ignition point to the squish zone, thereby reducing the flame propagation speed in the combustion chamber, There is an example in which the internal pressure rise is moderated. However, according to the configuration of the prior art, since the dome becomes deep, when the piston reaches the top dead center,
The air-fuel mixture compressed in the squish zone 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. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the related art, and has as its object to release shock applied to the piston top surface and emission of noise to the outside without reducing output. It is an object of the present invention to provide a two-cycle water-cooled engine for motorcycles, which can reduce noise and reduce noise. Means for Solving the Problems In order to achieve the above object, the present invention provides a dome which is coaxially located on a center line of a cylinder and has a circular cross section along a radial direction of the cylinder. Spreads toward the outer periphery of the piston top surface continuously with the opening of
A ring-shaped squish zone for compressing the air-fuel mixture and ejecting the mixture into the dome when the piston reaches the vicinity of the top dead center; a spark plug coaxially provided at the center of the apex of the dome; A two-cycle water-cooled engine for motorcycles having a combustion chamber in which the inner peripheral wall is inclined radially inward toward the spark plug side and the inclined surface is formed linearly along the axial direction of the dome. And, the distance from the center of the combustion chamber of the tightening bolt of the cylinder head having the squish zone and the dome is made longer on the exhaust port side than on the intake port side,
The thickness of the cylinder body is made thicker on the exhaust port side than on the intake port side, and 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 When the area of the concentric surface is S1 and the area of the ring-shaped surface obtained by subtracting the area S1 from the area of the plane passing through the maximum diameter portion of the squish zone is S2, the relationship of S2 / S1> 1.4 is defined. It is characterized by having done. According to this configuration, the squish zone is widened with respect to the dome close to the ignition point, and the amount of the air-fuel mixture that burns rapidly in the dome based on the squish effect is substantially reduced. It takes time for the flame to spread to the squish zone, which is considered to be less flammable than inside the dome, and the flame propagation speed in the combustion chamber becomes slower. As a result, the pressure in the cylinder increases gradually with respect to the crank angle, and accordingly, the impact applied to the piston top surface is reduced. Accordingly, the vibration of the piston is reduced, so that the resonance of the cylinder block and the crack case can be prevented, and the noise from around the engine can be reduced. Moreover, since the dome becomes narrower as the squish zone becomes wider, the air-fuel mixture compressed in the squish zone spreads to every corner of the dome when the piston reaches the top dead center. For this reason, even if the ignition rate is high and the flame propagation speed is low, the pressure in the cylinder rises to the same value as before, and it is possible to simultaneously secure the output in the high rotation range. Also, the distance from the combustion chamber center of the tightening bolts of the cylinder head is made longer on the exhaust port side than on the intake port side, and the thickness of the cylinder body is made thicker on the exhaust port side than on the intake port side. However, the combustion noise to the outside via the cylinder head is reduced, and the combustion noise to the outside via the cylinder body is reduced at the exhaust port side, which is the thick part, so that the combustion noise is more directional. You can have. FIG. 1 to FIG. 7 show a first embodiment of the present invention. In FIGS. 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. An intake port 4, an exhaust port 5, and a scavenging port 6 opened and closed by a piston 3 are opened on the inner peripheral surface of the cylinder 1a.
Through the crankcase 8 in the crankcase 8. A combustion chamber 9 is formed at the top of the cylinder 1a between the top surface 3a of the piston 3 and the opposing surface 2a of the cylinder head 2 when the piston 3 reaches near the top dead center. The combustion chamber 9 is located on the center line O1-O1 of the cylinder 1a, and has a circular dome 10 in cross section along the radial direction of the cylinder 1a.
And the top surface of the piston 3 continuously to the opening of the dome 10.
Ring-shaped squish zone spreading toward the outer circumference of 3a
The squish surface 11a facing 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 in the squish zone 11 is jetted into the dome 10, and the flow of the air-fuel mixture in the dome 10 is promoted. At the boundary between the dome 10 and the squish zone 11, a step 14 is formed continuously in the circumferential direction. A spark plug 12 is coaxially screwed into the tip surface 10a of the dome 10, and the diameter L1 of the tip surface 10a is formed to be substantially equal to the diameter of the screw portion 13 of the spark plug 12. Also,
The inner peripheral surface of the dome 10 forms an inclined surface 10b inclined inward in the radial direction as it proceeds toward the spark plug 12 side, and the boundary between the inclined surface 10b, the tip surface 10a and the squish zone 11 is a smooth curved surface. 10c, 10c
Between the curved surfaces 10c, 10c on the inclined surface 10b, a straight portion 10d is formed along the axial direction of the dome 10 over a predetermined length h. In the combustion chamber 9 having such a configuration, as shown in FIG. 1, 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 When the area of the concentric surface is S1 and the area of the ring-shaped surface obtained by subtracting the area S1 from the area of the maximum diameter (bore diameter) of the squish zone 11 is S2, the relationship of S1 <S2 is defined. Have been. 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, and engine coolant flows through the water jacket 16. By the way, the present inventor conducted an experiment for measuring the engine noise in each case by changing the area ratio S2 / S1 between the areas S1 and S2 in a two-cycle single-cylinder water-cooled engine having an inner diameter × a stroke of 56 × 50 mm. went. In this experiment, the measurement position of the noise was set to 50 mm on the side of the cylinder. FIG. 3 shows the results of the experiment, and it was confirmed that the relationship of S1 <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 in the dome 10 Since the amount of the air-fuel mixture that burns rapidly is substantially reduced, the flame that grew in the dome 10 in combination with the presence of the step 14 is transmitted to the squish zone 11, which is less flammable than in the dome 10. It is considered that it takes time and the flame propagation speed in the combustion chamber 9 becomes slow. As described above, when the flame propagation speed decreases, the pressure in the cylinder 1a increases gradually with respect to the crank angle, and the impact applied to the top surface 3a of the piston 3 can be reduced. Moreover,
If the area S1 is small, the portion where the pressure applied to the piston 3 is large becomes the narrow range of the central portion 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 as shown in FIG. 4 was obtained. As is evident 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 shown by the broken line, but there is hardly any difference in the change in the cylinder internal pressure. That is, the reason is that, when the inside of the dome 10 becomes narrow, when the piston 3 reaches the top dead center, the air-fuel mixture compressed in the squish zone 11 goes to every corner in the dome 10. It is considered that the squish effect is sufficiently exhibited. Therefore, even if the propagation speed of the flame is low, the ignition rate is high and the propagation of the flame is performed smoothly to the air-fuel mixture at the end in the squish zone 11, so the cylinder internal pressure increases to the same value as before, and the high rotation speed The output in the area can be secured at the same time. As is clear from FIGS. 5 and 7, the distance from the center of the combustion chamber 9 to the hole 18 of the tightening bolt 17 on the exhaust port 5 side of the cylinder head 2 having the squish zone 11 and the dome 10 depends on the intake air. It is longer than the holes 19 on the mouth 4 side (see FIG. 7). Further, the thickness of the cylinder body 1 is configured to be thicker on the exhaust port 5 side than on the intake port 4 side (see FIG. 7). Therefore, the position of the bolt 17 on the exhaust port 5 side for tightening the cylinder head 2 is shifted from the center of the combustion chamber 9 as compared with the other bolts, and the pressure due to combustion is reduced from the antinode of the vibration mode of the cylinder foot 2. It will act on the position shifted to the side, and if the input is the same, its amplitude will decrease,
As a result, the combustion noise emitted to the outside through the cylinder head 2 is reduced. Further, since the thickness of the cylinder body 1 is made thicker on the exhaust port 5 side, the combustion noise emitted to the outside through the cylinder body 1 has high and low levels, and the emission of noise from the exhaust port 5 side is reduced. Can be. Therefore, the combustion noise can be reduced on the exhaust port 5 side as compared with the air port 4 side which has a noise prevention effect due to the arrangement of peripheral parts (carburetor, air cleaner, etc.) in a normal motorcycle.
In addition, the water jacket 16 on the exhaust port 5 side can be larger in the vicinity of the combustion chamber 9 than the water jacket 16 on the intake port 4 side in relation to the position of the tightening bolts 17. Exhaust port 5 that tends to be
Can be effectively cooled. Thus, by taking into account the tightening of the cylinder head 2 and the thickness of the cylinder body 1 in the structure of the combustion chamber 9 described above, a two-stroke water-cooled engine for motorcycles capable of suppressing noise even lower is obtained. The dimensions of the combustion chamber and the shape of each part are not specified in the above embodiment. For example, as in the second embodiment of the present invention shown in FIG. 8, the inclined surface 10b and the tip surface 10a are connected. curved surface
The radius R of the tip 10c is made larger, the diameter L1 of the tip surface 10a is made larger than the diameter of the screw portion 13 of the spark plug 12, and the inclination of the squish surface 11a is made smaller to the contrary, and the straight portion 10d is formed.
May be increased while the angle θ is increased. Also, as in the third embodiment of the present invention shown in FIG.
The length h of d may be increased, and if the relationship of S2 / S1> 1.4 is satisfied with the depth kept constant without increasing the depth of the combustion chamber, the length of the inclined surface or the curved surface Can be changed as appropriate. According to the present invention described in detail above, the flame propagation speed is reduced in the combustion chamber, and the pressure in the cylinder is gradually increased. Noise can be kept low. Moreover,
When the piston reaches the top dead center, the air-fuel mixture compressed in the squish zone spreads to every corner of the dome,
The original squish effect is fully exhibited, and output in a high rotation range can be secured at the same time. The noise can be suppressed low by taking into account the tightening of the cylinder head and the thickness of the cylinder body in the structure of the combustion chamber. It becomes a two-cycle water-cooled engine for motorcycles.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 7 show a first embodiment of the present invention.
The figure is a configuration diagram showing the cross-sectional shape of the combustion chamber, and FIG. 2 is a view in FIG.
3 and 4 are characteristic diagrams, respectively, FIG. 5 is a cross-sectional view of a two-cycle water-cooled engine for a motorcycle, and FIG. 6 is a line VI-VI in FIG. Cross section along the seventh
FIG. 8 is a bottom view of the cylinder head, FIG. 8 is a configuration diagram showing the shape of the combustion chamber of the second embodiment of the present invention, and FIG.
It is a lineblock diagram showing a combustion chamber shape of an example. 1 ... cylinder body, 1a ... cylinder, 2 ... cylinder head, 3 ... piston, 3a ... top surface, 4 ... intake port, 5 ... exhaust port, 9 ... combustion chamber, 10 ... dome , 10b
... Slope, 11 Squish zone, 12 Spark plug, 17 Tightening bolt.

Claims (1)

(57) [Claims] While being coaxially located on the center line of the cylinder,
A dome having a circular cross section along the radial direction of the cylinder and a dome that is continuous with the opening of the dome toward the outer peripheral side of the piston top surface, and when the piston reaches the vicinity of the top dead center, the air-fuel mixture is released. A ring-shaped squish zone to be compressed and ejected into the dome, and a spark plug is provided coaxially at the center of the apex of the dome,
The two-stroke water-cooled engine for a motorcycle 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, The distance from the center of the combustion chamber of the tightening bolt of the cylinder head with the squish zone and the dome is longer on the exhaust port side than on the intake port side, and the thickness of the cylinder body is smaller than on the intake port side. The exhaust port side is made thicker, and the area of the 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 is S1, the area of the squish zone is When the area of the ring-shaped surface obtained by subtracting the area S1 from the area of the plane passing through the maximum diameter portion is defined as S2, the relationship is defined as S2 / S1> 1.4. Two-cycle water-cooled engine for motorcycles.