JP2534647B2 - Two-cycle engine combustion chamber - Google Patents

Description

The present invention relates to a two-stroke engine, and more particularly to the structure of its combustion chamber.

[Prior art]

Conventionally, in a combustion chamber of a two-cycle engine, a dome facing a spark plug is provided at a certain angle with respect to a center line of a cylinder, and a ring-shaped squish zone extending toward an outer peripheral side of a piston top surface is continuously provided on the dome. When the piston reaches near top dead center, the mixture is compressed in the squish zone and ejected into the dome,
It is known that the ignition rate and flame propagation speed are increased by concentrating the air-fuel mixture in the dome.

However, if the flame propagation speed is increased in this way, the pressure in the cylinder rapidly rises, so that the impact applied to the top surface of the piston becomes particularly large. Therefore, there is a problem that the engine vibration becomes large, such that the piston vibrates due to this impact, and the vibration of the piston is transmitted to the cylinder block and the crankcase to resonate with each other to generate an unpleasant resonance sound.

As a countermeasure against this, conventionally, the sloping surface of the dome, which is inclined inward as it goes to the spark plug side, is formed longer to increase the distance from the ignition point to the squish zone to slow the flame propagation speed in the combustion chamber, There is an example in which the pressure rise inside is moderated.

[Problems to be solved by the invention]

However, according to the configuration of the prior art, the dome is deepened, so that when the piston reaches the top dead center,
The air-fuel mixture compressed in the squish zone does not reach the vicinity of the spark plug sufficiently.

Therefore, although the noise is reduced, the original squish effect is impaired, which causes a problem such as a reduction in output in a high rotation range.

The present invention has been made based on such a situation, and while sufficiently securing the squish effect, noise from around the combustion chamber can be suppressed to a small level, and the thermal balance in the combustion chamber becomes good. The purpose is to provide a combustion chamber of a two-cycle engine capable of preventing abnormal combustion.

[Means for solving problems]

In order to achieve the above object, the present invention provides a dome having a circular cross-section along the radial direction of the cylinder and a dome extending continuously toward the outer peripheral side of the piston top surface so that the piston reaches the vicinity of top dead center. And a ring-shaped squish zone for compressing the air-fuel mixture and ejecting it into the dome,
The axis line of the dome is provided at a certain angle with respect to the center line of the cylinder, the spark plug is coaxially provided at the center of the apex of the dome, and the inner wall of the dome is radially inward toward the spark plug side. It is inclined and this inclined surface is formed linearly along the axial direction of the dome. 2
It is premised on the combustion chamber of a cycle engine.

The axis of the dome is inclined from the top surface side of the piston toward the spark plug in a direction away from the exhaust port on the inner surface of the cylinder with respect to the center line of the cylinder, and the spark plug positioned on this axis is positioned. Is located on the opposite side of the exhaust port across the center line of the cylinder, and is surrounded by the intersection line of the extension line along the inclined surface of the dome and the plane passing through the maximum diameter part of the squish zone. Let S1 be the area of the elliptical surface and S2 be the area of the ring-shaped surface that is obtained by subtracting the area S1 from the area of the plane passing through the maximum diameter part of the squish zone. S1 <S2 It has a feature.

[Action]

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 rapidly burns based on the squish effect is substantially reduced, so that the flame propagation speed in the combustion chamber becomes slow. As a result, the pressure increase in the cylinder with respect to the crank angle is moderated, and the impact applied to the piston top surface is correspondingly reduced. Therefore, the vibration of the piston is reduced, and resonance around the cylinder block and the crankcase can be prevented,
The engine noise can be kept low.

Moreover, since the dome becomes narrower as the squish zone becomes wider, when the piston reaches the top dead center, the air-fuel mixture compressed in the squish zone reaches all the corners of the dome, which causes ignition. The rate is high and flame spread is smoothed to the end air-fuel mixture. Therefore, even if the flame propagation speed is slow, 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.

Further, according to the above configuration, since the electrode of the spark plug moves away from the exhaust port side where the temperature becomes high during engine operation due to the inclination of the dome, ignition of the air-fuel mixture occurs more than at the exhaust port side end of the combustion chamber. Done on the opposite side of the cylinder centerline. For this reason, the thermal balance in the combustion chamber becomes good, and accordingly, the flame grows stably, and abnormal combustion can be prevented.

Example of Invention

The first embodiment of the present invention will be described below with reference to FIGS. 1 to 7 applied to a two-cycle engine for a motorcycle.

In FIG. 5, reference numeral 1 is a cylinder block, 2 is a cylinder head, and a cylinder 1a is formed in the cylinder block 1. An intake port 4 and an exhaust port 5 are opened in the inner peripheral surface of the cylinder 1a so as to face each other in the radial direction, and a plurality of scavenging ports 6 are located between the intake port 4 and the exhaust port 5 ... ... are opened, and the intake port 4, the exhaust port 5 and the scavenging port 6 are opened and closed by the piston 3. The scavenging ports 6 ... Are connected to a crank chamber (not shown) in a crankcase through a scavenging passage 7.

At the top of the cylinder 1a, a combustion chamber 9 is formed between the top surface 3a of the piston 3 and the facing surface 2a of the cylinder head 2 when the piston 3 reaches near the top dead center. The combustion chamber 9 has a dome 10 having a circular cross section along the radial direction of the cylinder 1a, and a top surface 3a of the piston 3 continuous with the dome 10.
Ring-shaped squish zone 11 that extends toward the outer circumference of
And the piston 3 in this squish zone 11
The squish surface 11a facing the top surface 3a is inclined in a direction away from the top surface 3a as it goes radially inward. Therefore, in the compression stroke, when the piston 3 rises to near the top dead center, the air-fuel mixture compressed in the squish zone 11 is ejected 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 portion 14 continuous in the circumferential direction is formed, and the surface of the step portion 14 facing the combustion chamber 9 forms a smooth curved surface 14a.

By the way, the dome 10 of the present embodiment is positioned slightly eccentric to the intake port 4 side with respect to the center line o ₁ -o ₁ of the cylinder 1a. Moreover, as shown in FIG. 5, the dome 10 moves away from the exhaust port 5 with respect to the center line O1-O1 of the cylinder 1a as its axis O2-O2 moves away from the top surface 3a side of the piston 3. It is inclined at a constant angle α. dome
The tip surface 10a of 10 is substantially orthogonal to the axis O2-O2, and the screw portion 13 of the ignition plug 12 is screwed into the tip surface 10a. The spark plug 12 is the axis O2− of the dome 10.
It is arranged coaxially with O2. Spark plug 12 electrode 12
a is located on the axis O2-O2 of the dome 10, and this electrode 12a is, as shown in FIG. Is located in.

The diameter L1 of the tip surface 10a of the dome 10 is
It is formed to have a diameter substantially equal to that of the screw portion 13. Further, the inner peripheral surface of the dome 10 forms an inclined surface 10b which is inclined inward in the radial direction as it goes to the spark plug 12 side.
The boundary portion between the tip surface 10a and the tip surface 10a is connected by a curved surface 10c having a radius R, and between the curved surfaces 10c and 14a on the inclined surface 10b, in the axial direction of the dome 10 over a certain length h. A straight line portion 10d is formed along the straight line portion 10d. In this case, the length h of the straight portion 10d is continuously changed in the circumferential direction as the dome 10 itself is inclined.

In the combustion chamber 9 having such a configuration, as shown in FIG. 1, an elliptical shape surrounded by an intersection line between an extension line along the inclined surface 10b of the dome 10 and a plane passing through the maximum diameter portion of the squish zone 11. Face area S ₁ , and squish zone
When 11 maximum diameter area (bore diameter) portion area from the rings obtained by subtracting the area S ₁ surface of the set to S _2, are defined in relation S ₁ <S _2.

By the way, the present inventor measures the engine noise in each case by changing the area ratio S ₂ / S ₁ 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. An experiment was conducted. In this experiment, the noise measurement position was set to 50 mm lateral to the cylinder.

Fig. 3 shows the measurement results. It was confirmed that the engine noise drastically decreased from the conventional level when the relationship of S ₁ <S ₂ was established, that is, when the area ratio exceeded 1.4. .

That is, the reason is that if the relationship between the areas S ₁ and S ₂ is defined as described above, the squish zone 11 in which the air-fuel mixture is less likely to burn becomes wider than the dome 10, so that the dome 10 is based on the squish effect. The amount of air-fuel mixture that burns rapidly in the squish zone 11
It is considered that it takes time to reach the inside and the flame propagation speed in the combustion chamber 9 becomes slow.

In this way, when the flame propagation speed becomes slow, the pressure increase 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 S ₁ 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 combination with the reduction of the impact. Therefore, resonance around the cylinder block 1 and the crankcase 8 can be prevented, and engine noise can be suppressed to a low level.

The present inventor investigated the angle θ formed by the extension line of the inclined surface 10b and the reference line orthogonal to the axis line o ₂ -o _{2 of the} dome 10 in the combustion chamber 9 in which a sharp decrease in engine noise was observed. As a result, it became clear that when the relationship of S ₁ <S ₂ holds, θ becomes 61 ° or more. Therefore, in order to efficiently reduce the engine noise, the area ratio S ₂ / S _{1 is set} to 2 or more and the inclination angle θ of the inclined surface 10b is set to 70 or less.
It is desirable that the angle be at least °.

On the other hand, when the inventor examined the change in the cylinder internal pressure with respect to the crank angle when the combustion chamber 9 had the above-described shape, the results shown in FIG. 4 were obtained. As is clear from FIG. 4, the time point at which the internal pressure becomes maximum is slightly shifted to the bottom dead center side as compared with the conventional case shown by the broken line, but there is almost no difference in the change in the cylinder internal pressure.

That is, the reason for this is that as the inside of the dome 10 becomes narrower, when the piston 3 reaches the top dead center, the air-fuel mixture compressed in the squish zone 11 reaches every corner of the dome 10. It is thought that this is because the squish effect is fully exerted. Therefore, even though the propagation speed of the flame is slow, the ignition rate is high, and the flame grows smoothly to the air-fuel mixture at the end in the squish zone 11, and as a result, the cylinder pressure rises to a value equivalent to the conventional value. become,
It is possible to secure the output in the high rotation range at the same time.

In addition, according to the above configuration, since the axis O2-O2 of the dome 10 is inclined, the electrode 12a of the spark plug 12 that is the ignition point for the air-fuel mixture moves away from the exhaust port 5 side that becomes hot during engine operation. The ignition of the air-fuel mixture is performed on the opposite side of the center line O1-O1 of the cylinder 1a from the end of the combustion chamber 9 on the exhaust port 5 side. Therefore, the thermal balance in the combustion chamber 9 becomes good, the flame grows stably, and abnormal combustion can be prevented.

The size of the combustion chamber and the shape of each part are not limited to the above-described embodiment, and the curved surface 10c connecting the inclined surface 10b and the tip end surface 10a as in the second embodiment shown in FIG. The radius R may be made larger, or the inclination angle α of the dome 10 with respect to the center line o ₁ -o ₁ of the cylinder may be made larger as in the third embodiment shown in FIG.

Furthermore, the two-cycle engine according to the present invention is not limited to motorcycles, and can be applied to other vehicles and various fields other than vehicles.

〔The invention's effect〕

According to the present invention described in detail above, since the impact applied to the top surface of the piston is reduced, the vibration of the piston is suppressed, so that the resonance around the cylinder block and the crankcase can be prevented, and the noise of the engine can be suppressed to a low level. it can.
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, so the original squish effect is fully exerted and the output in the high rotation range is also achieved. Can be secured at the same time.

Also, as the electrode of the spark plug moves away from the exhaust port side, which becomes hot during engine operation, due to the inclination of the dome, ignition of the air-fuel mixture will occur at the center line of the cylinder relative to the exhaust port side end of the combustion chamber. Done on the opposite side of the way. Therefore, there is an advantage that the thermal balance in the combustion chamber becomes good, the flame grows stably, and abnormal combustion can be prevented.

[Brief description of drawings]

1 to 7 show a first embodiment of the present invention.
FIG. 2 is a configuration diagram showing the cross-sectional shape of the combustion chamber, FIG. 2 is a diagram showing the relationship between the areas S ₁ and S _{2 in} the maximum diameter portion of the combustion chamber, and FIGS. 3 and 4 are characteristic diagrams respectively. FIG. 5 is a cross-sectional view of a two-cycle engine, FIG. 6 is a plan view of a cylinder head, FIG. 7 is a schematic view showing a positional relationship among intake, exhaust and scavenging ports,
FIG. 9 is a configuration diagram showing the shape of the combustion chamber of the first embodiment of the present invention, and FIG. 9 is a configuration diagram showing the shape of the combustion chamber of the third embodiment of the present invention. 1a ... Cylinder, 2 ... Cylinder head, 3 ... Piston, 3a ... Top surface, 5 ... Exhaust port, 9 ... Combustion chamber, 10 ...
Dome, 10b …… Slope, 11 …… Squish zone, 12
...... Spark plug, 12a ...... Electrode.

Claims (1)

(57) [Claims] 1. A dome having a circular cross-section along the radial direction of the cylinder, and a dome extending continuously toward the outer peripheral side of the piston top surface, and when the piston reaches the vicinity of top dead center, the air-fuel mixture is mixed. And a ring-shaped squish zone for compressing and ejecting into the dome, the axis of the dome is inclined at a certain angle with respect to the center line of the cylinder, and the spark plug is coaxially provided at the center of the apex of the dome. In the combustion chamber of a two-cycle engine, the inner wall of the dome is inclined radially inward as it goes to the spark plug side, and the inclined surface is linearly formed along the axial direction of the dome. The axis line of the piston is inclined from the top surface side of the piston toward the spark plug in the direction away from the exhaust port on the inner surface of the cylinder with respect to the center line of the cylinder. The electrode of the spark plug located above is located on the opposite side of the exhaust port across the center line of the cylinder, and a plane passing through the extension line along the inclined surface of the dome and the maximum diameter part of the squish zone. Let S1 be the area of the elliptical surface surrounded by the line of intersection with, and S2 be the area of the ring-shaped surface obtained by subtracting the area S1 from the area of the plane passing through the maximum diameter part of the squish zone. A combustion chamber of a two-cycle engine characterized by the above-mentioned relationship.