JP2916145B2 - Combustion chamber of two-stroke water-cooled engine - Google Patents

Description

The present invention relates to a two-stroke water-cooled engine, and more particularly to a structure of a combustion chamber thereof. [Prior Art] In a combustion chamber of a two-stroke water-cooled engine, conventionally,
For example, as seen in "JP-A-51-29622",
A ring-shaped squish zone that continuously extends toward the outer periphery of the piston top surface is continuously provided on the dome facing the spark plug, and when the piston reaches near the top dead center, the air-fuel mixture is compressed in the squish zone and the dome is compressed. The fuel is injected into the dome and the air-fuel mixture is concentrated in the dome, so that the ignition rate and the fire propagation speed are increased, and the output is pushed forward. Conventionally, a so-called offset dome in which the dome is eccentric with respect to the cylinder center line has been known in order to further promote the ignitability and the growth of the flame in the dome. However, when the flame propagation speed is increased by using the offset dome and the squish effect as described above, the pressure in the cylinder sharply increases, so that the impact particularly applied to the piston top surface increases. Therefore, the shock causes the piston to vibrate and the vibration of the piston to be transmitted to the cylinder and the crankcase, causing the resonance of the piston and an unpleasant resonance sound. As a countermeasure against this, conventionally, the dome sloped inward as it progressed toward the spark plug side was formed longer, increasing the distance from the ignition point to the squish zone to reduce the flame propagation speed in the combustion chamber, There is an example in which the internal pressure rise is moderated. [Problems to be Solved by the Invention] However, according to the configuration of the prior art, since the dome is deepened, when the piston reaches the vicinity of the top dead center, the air-fuel mixture compressed in the squish zone is used for the ignition plug. It does not reach the vicinity sufficiently. Therefore, although the noise is reduced, the original squish effect is impaired, and disadvantages such as a decrease in output in a high rotation speed range occur. The present invention has been made in view of such circumstances, and it is possible to reduce the impact applied to the piston top surface without lowering the output, and to reduce the noise level of the combustion chamber of a two-cycle water-cooled engine. The purpose is to provide. [Means for Solving the Problems] In order to achieve the above-described problems, the present invention is directed to a cylinder having a circular shape having a cross-sectional shape along the radial direction of the cylinder, which is positioned eccentric to the intake port side with respect to the center line of the cylinder. With the dome, the dome spreads from the entire periphery of the open end toward the outer periphery of the piston top surface, and when the piston reaches near the top dead center,
A ring-shaped squish zone for compressing the air-fuel mixture and jetting the mixture into the dome. A spark plug is provided coaxially at the center of the apex of the dome, and the inner peripheral wall of the dome is closer to the spark plug than the opening end. It is premised on the combustion chamber of a two-stroke water-cooled engine, which is inclined inward in the radial direction as it goes to, and this inclined surface is formed linearly along the axial direction of the dome, and the displacement is approximately 123 cc. In the present invention, the area of a surface concentric with the dome surrounded by an intersection of an extension line along the inclined surface of the dome and a plane passing through the largest diameter portion of the squish zone is S1, and the area of the squish zone is When the area of the ring-shaped surface obtained by subtracting the above 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. [Operation] According to this configuration, the squish zone is widened with respect to the dome near the ignition point, and the amount of the air-fuel mixture that burns rapidly based on the squish effect is substantially reduced. Therefore, it takes time for the flame grown in the dome to spread to the squish zone, which is more difficult to burn than in the dome, and the flame propagation speed in the combustion chamber is reduced.
As a result, the pressure rise in the cylinder with respect to the crank angle becomes gentle, and accordingly, the impact applied to the piston top surface is reduced. Therefore, since the vibration of the piston is reduced, resonance around the cylinder block and the crankcase can be prevented, and the noise of 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. Therefore, in addition to the eccentricity of the dome, the ignition rate of the air-fuel mixture is increased, and the flame is smoothly propagated to the terminal air-fuel mixture. For this reason, even if the flame propagation speed is low, the pressure in the cylinder rises to the same value as before, and the output in the high rotation range can be secured at the same time. [Embodiment of the Invention] Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 7 in which the present invention is applied to a two-cycle water-cooled engine for a motorcycle. In FIG. 5, reference numeral 1 denotes a cylinder block, 2 denotes a cylinder head, and a cylinder 1a is formed in the cylinder block 1. As shown in FIG. 7, an intake port 4, an exhaust port 5 and a plurality of scavenging ports 6 are provided on the inner peripheral surface of the cylinder 1a.
Is open. The intake port 4 and the exhaust port 5 are cylinders
They are arranged so as to face each other in the radial direction of 1a. The scavenging port 6 is located between the intake port 4 and the exhaust port 5, and these scavenging ports 6 communicate with a crank chamber (not shown) in a crankcase through a scavenging passage 7. The intake port 4, the exhaust port 5, and the scavenging port 6
Is opened and closed by the piston 3. 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 eccentric to the intake port 4 side by a predetermined distance X with respect to the center line O1-O1 of the cylinder 1a, and has a circular cross section along the radial direction of the cylinder 1a.
A ring-shaped squish zone 11 is provided which extends from the entire periphery of the open end of the piston 10 toward the outer periphery of the top surface 3a of the piston 3. Top surface of piston 3 in squish zone 11
The squish surface 11a facing the surface 3a 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. A step 14 is formed at the boundary between the dome 10 and the squish zone 11 and is continuous in the circumferential direction. The surface of the step 14 facing the combustion chamber 9 has a smooth curved surface 14a. An ignition plug 12 is coaxially screwed into the tip end surface 10a of the dome 10. The diameter of the tip surface 10a is set to be substantially equal to the diameter of the screw portion 13 of the spark plug 12. Further, the inner peripheral surface of the dome 10 forms an inclined surface 10b which is inclined radially inward toward the spark plug 12 side. The boundary between the inclined surface 10b and the tip surface 10a has a radius R
Between the curved surfaces 10c and 14a on the inclined surface 10b over a certain length h.
A linear portion 10d is formed along the axial direction of the ten. In this case, the length h of the straight portion 10d is continuously changed in the circumferential direction with the eccentricity of the dome 10. In the combustion chamber 9 having such a configuration, as shown in FIG. 1, the dome 10 is 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 obtained. Stipulated. As shown in FIGS. 5 and 6, the cylinder block 1 and the cylinder head 2 include a water jacket 16 surrounding the cylinder 1a and the combustion chamber 9, and the water jacket 16 is used to cool the engine. Water is flowing. By the way, the present inventor, in the two-stroke single-cylinder water-cooled engine of the inner diameter × stroke is 56 × 50 mm, the displacement obtained from this inner diameter × stroke is approximately 123 cc, the area ratio S2 / S1 of the area S1 and S2 Experiments were conducted in which the engine noise was measured in each case. In this experiment, the measurement position of the noise was 50 mm on the side of the cylinder 1a. FIG. 3 shows the measurement results. When the relationship of S1 <S2 is satisfied, that is, when the area ratio exceeds 1.4,
The fact that the engine noise sharply decreased from the conventional level was recognized. 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 in which the air-fuel mixture is less likely to burn than the dome 10 becomes wider. Accordingly, the amount of the air-fuel mixture that burns rapidly in the dome 10 based on the squish effect is substantially reduced. For this reason, it is considered that it takes time for the flame grown in the dome 10 to propagate to the squish zone 11 in combination with the presence of the step portion 14, and the flame propagation speed in the combustion chamber 9 is reduced. When the flame propagation speed is reduced in this manner, the pressure in the cylinder 1a relative to the crank angle rises moderately, and the impact applied to the top surface 3a of the piston 3 is reduced. Moreover, if the area S1 is small, the portion where the pressure applied to the piston 3 is large is a narrow range of the central portion of the top surface 3a.
Combined with the reduction of the impact, the vibration of the piston 3 is suppressed. Therefore, resonance of the cylinder block 1 and the crankcase can be prevented, and the noise of the engine can be reduced. In addition, the present inventor examined the angle θ between the extension of the inclined surface 10b and the plane of the maximum diameter portion of the squish zone 11 in the combustion chamber 9 where the engine noise was sharply reduced. When the relationship of S2 / S1> 1.4 holds, it has been found that θ is 61 ° or more.
Therefore, in order to reduce the engine noise efficiently, it is desirable that the area ratio S2 / S1 is 2 or more and the inclination angle θ of the inclined surface 10b is 70 ° or more. 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 apparent from FIG. 4, although the point at which the internal pressure becomes maximum slightly shifts toward the bottom dead center side as compared with the conventional case shown by the broken line, there is hardly any difference in the change in the cylinder internal pressure. That is, the reason is that when the piston 3 reaches the top dead center as the inside of the dome 10 becomes narrower, the air-fuel mixture compressed in the squish zone 11 spreads to every corner in the dome 10. It is considered that the squish effect is sufficiently exhibited. Therefore, even if the flame propagation speed is slow,
In addition to the fact that the dome 10 is eccentric to the intake port 4 side, the ignition rate is high, and the growth of the flame is smoothly performed up to the air-fuel mixture at the end in the squish zone 11. As a result, the cylinder internal pressure rises to a value equivalent to the conventional value, and the output in a high rotation range can be secured at the same time. Note that 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. curved surface
The radius R of the tip 10c is made larger, the diameter L1 of the tip face 10a is made larger than the diameter of the threaded portion 13 of the spark plug 12, and the inclination of the squish face 11a is made smaller to increase the angle θ. May be. Further, as in the third embodiment of the present invention shown in FIG. 9, the radius R of the curved surface 10c on the side of the distal end surface 10a is reduced, and
The length h of d may be longer than that of the second embodiment. If the relationship of S2 / S1> 1.4 is satisfied, the length of the inclined surface, the curvature of the curved surface, the angle θ, and the like are appropriately changed. It is possible. Furthermore, the two-stroke water-cooled engine according to the present invention is not limited to motorcycles, and can be applied to other vehicles and various fields other than vehicles. [Effects of the Invention] According to the present invention described in detail above, the impact applied to the piston top surface is reduced, and the vibration of the piston is suppressed, so that resonance around the cylinder block and the crankcase can be prevented, and the engine Noise can be kept low. In addition, when the piston reaches near the top dead center, the air-fuel mixture compressed in the squish zone spreads to every corner of the dome, so the squish effect is fully exhibited and the output in the high rotation range is secured at the same time There is an advantage that it can be done.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 to FIG. 7 show a first embodiment of the present invention, FIG. 1 is a configuration diagram showing a sectional shape of a combustion chamber, and FIG. FIG. 3 is a graph showing the relationship between the area S1 and S2 in the radial portion, FIG. 3 is a graph showing the noise reduction ratio of the engine, and FIG. 4 is a graph showing how the internal cylinder pressure changes with respect to the crank angle. 5 is a cross-sectional view of a two-stroke water-cooled engine, FIG. 6 is a plan view of a cylinder head, FIG. 7 is a schematic view showing a positional relationship between an intake port, an exhaust port, and a scavenging port. FIG. 9 is a configuration diagram showing a combustion chamber shape according to a second embodiment of the present invention. FIG. 9 is a configuration diagram showing a combustion chamber shape according to a third embodiment of the present invention. 1a cylinder, 2 cylinder head, 3 piston, 3a top surface, 4 intake port, 9 combustion chamber, 10 dome, 10b inclined surface, 11 squish zone , 12 ... Spark plug.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02B 23/00-25/28 F02F 1/00-3/28

Claims (1)

(57) [Claims] A circular dome, which is eccentric to the intake port side with respect to the center line of the cylinder and has a circular cross section along the radial direction of the cylinder; and from the entire periphery of the open end of the dome to the outer peripheral side of the piston top surface. And 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 is provided coaxially at the center of the apex of the dome. ,
The inner peripheral wall of the dome is inclined radially inward as going from the opening end toward the spark plug side, and the inclined surface is formed linearly along the axial direction of the dome, and the displacement is approximately 123 cc. In the combustion chamber of the two-stroke water-cooled engine, the area of a surface concentric with the dome, which is surrounded by an intersection of an extension line along the inclined surface of the dome and a plane passing through a maximum diameter portion of the squish zone, is S1, Combustion of a two-stroke water-cooled engine characterized by the relationship of S2 / S1> 1.4, where S2 is the area of the ring-shaped surface obtained by subtracting the above S1 from the area of the plane passing through the maximum diameter portion of the squish zone. Room.