JPH0122904Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a combustion chamber for a two-stroke engine, which is constructed by integrally connecting a cylinder head to a cylinder block with a gasket interposed therebetween.

Prior Art The combustion of the air-fuel mixture that takes place in the combustion chamber is an intermittent combustion in which ignition and subsequent fire propagation are repeated in short cycles, and the chemical energy of combustion is converted into thermal energy in this combustion engine, which drives the piston movement. The rotational work is taken out to the crankshaft through the motor.

Combustion of the mixture is intermittent, and the mixture condition changes significantly from idling to full load, so it is necessary to ensure ignition stability and normal flame propagation characteristics to ensure stable engine performance. becomes. These are closely related to the diffusion of the air-fuel mixture within the combustion chamber, the shape of the combustion chamber, and the position of the spark plug.

Among the factors that affect combustion, the shape of the combustion chamber and the position of the spark plug have a large effect on combustion.

In two-stroke engines in which a cylinder head is integrally connected to a cylinder block through a gasket, a hemispherical combustion chamber, etc., as shown in FIG. 1, has been widely used. In FIG. 1, 01 is the engine body, and the cylinder 02
The cylinder head 03 is connected to the upper end of the cylinder 02, and the spark plug 04 and the piston 05 are screwed onto the cylinder head 03.

A substantially hemispherical recess 06 is formed at the bottom of the cylinder head 03, and a protrusion 07 with a predetermined curvature R is formed at the top of the piston 05 facing the recess 06. The space defined by is a combustion chamber 08 having a predetermined volume. The ignition point 09 of the ignition plug 04 is located at the top of the substantially hemispherical combustion chamber 08.

Furthermore, although it is a four-stroke engine, as shown in FIG. forming a shaped recess 015;
The ignition point 01 of the ignition plug 017 is located at the center of the spherical combustion chamber 016 formed by the recesses 013 and 015.
There was one where 7a was positioned. Note that 018 and 019 are an exhaust valve and an intake valve, respectively. (Refer to Japanese Unexamined Patent Publication No. 51-89911) Problems to be solved by the invention In the one shown in FIG. The depth is increased, and as a result, the height of the spark plug 04 is increased, and the height of the engine 01 is also increased. In addition, the difference between the ignition point and the combustion chamber wall was large, which was unfavorable in terms of combustion efficiency.

In addition, in the case shown in Figure 2, the combustion pressure acts perpendicularly to the entire inner wall surface, and on the piston, this pressure acts as a force that expands the top in the radial direction, making it easy for seizures to occur, and furthermore, the overall The component force in the radial direction of the piston increases and the component force in the sliding direction becomes small, which has the disadvantage that it is difficult to increase the output.Furthermore, this increase in the component force of the combustion pressure in the radial direction of the piston is caused by the cylinder block. This increases the pressure load on the gasket interposed between the cylinder head and the cylinder head, resulting in problems such as blow-through and the like. Furthermore, since the peripheral edge of the concave portion of the piston is formed at an acute angle and is not a curved surface, when the piston moves downward from top dead center, the flow of combustion gas in the combustion chamber along the flat lower surface of the cylinder head and the flat top surface of the piston is prevented. Turbulence occurs and combustion does not occur smoothly, making it difficult to increase output and improve fuel efficiency.

Means and Effects for Solving the Problems The present invention relates to an improvement of the combustion chamber structure of a two-stroke engine that overcomes the above-mentioned difficulties, and aims to improve the combustion chamber structure of a two-stroke engine in which a cylinder head is integrally connected to a cylinder block. In the chamber, the cylinder head and the cylinder block have mating surfaces that are integrally joined via a gasket, and the cylinder head has the deepest recess at the center of the top of the cylinder hole, and the deepest recess at the center of the top of the piston. A recess is formed in the piston to form a combustion chamber, and the radius of curvature of the center portion of the piston recess is set to be larger than the radius of curvature of the center portion of the cylinder head recess, and the ignition point of the ignition plug is set between the cylinder block and the cylinder head. deviated toward the cylinder head side in the cylinder axial direction than the mating surfaces of the cylinder block and the cylinder head, and peripheral portions of the two recesses are formed into curved surfaces that gently and smoothly connect to the mating surfaces of the cylinder block and the cylinder head. The combustion chamber structure of the two-stroke engine is characterized by:

In the present invention, the radius of curvature of the center portion of the piston recess is set to be larger than the radius of curvature of the center portion of the cylinder head recess, and the ignition point of the spark plug is positioned above the mating surface of the cylinder block and cylinder head. Therefore, the flame front of the air-fuel mixture generated by ignition with the spark plug and the accompanying shock wave do not directly reach the gasket interposed in the mating surface of the cylinder block and cylinder head.
In addition, in the present invention, the peripheral portions of both of the recesses are formed into curved surfaces that connect gently and smoothly to the mating surfaces of the cylinder block and cylinder head, so that the mixture that is ignited by the ignition plug and causes combustion. The combustion gases flow smoothly from the center of the wall surface of the combustion chamber on the cylinder head side and the center of the wall surface of the combustion chamber on the piston side without causing any turbulence along the respective wall surfaces, and as a result, combustion is carried out smoothly in a short time.

Embodiment An embodiment of the present invention illustrated in FIG. 3 will be described below.

1 is an engine body, and the engine body 1 includes a cylinder block 2, a cylinder head 3 connected to the upper end of the cylinder block 2 via a gasket 6, and a spark plug 4 screwed onto the cylinder head 3. , a piston 5, etc., which are slidably fitted into the cylinder block 2.

At the bottom of the cylinder head 3, there is formed a recess 7, which has a substantially hemispherical shape and is connected gently and smoothly to the mating surface with the cylinder block 2. A recess 8 is formed which has a larger diameter than the recess 7 of the cylinder head 3 and has a nearly hemispherical shape that connects gently and smoothly toward the mating surfaces of the cylinder block 2 and the cylinder head 3. The space defined by 8 is a flat spherical combustion chamber 9 having a predetermined volume. The gap between the outer periphery of the concave portion 7 of the cylinder head 3 and the outer periphery of the top of the piston 5 forms a squishing portion 10, and combustion occurs from the squishing portion 10 by utilizing the relative movement between the cylinder head 3 and the piston 5. It is designed to create a so-called squishing flow in which the air-fuel mixture is pushed out into the chamber 9 space (especially toward the ignition point 11) (normal squishing) or pulled back (reverse squishing).

Further, an ignition plug 4 is airtightly screwed onto the top of the recess 7 of the cylinder head 3, and an ignition point 11 located at a position where an outer electrode 4a and a center electrode 4b of the ignition plug 4 face each other forms a substantially spherical combustion. It is arranged to be located almost in the center of chamber 9. Note that the spark plug 4 is a two-pole plug with good ignitability.

Since the embodiment shown in FIG. 3 is constructed as described above, the shape of the combustion chamber 9 is a flat spherical shape.
Moreover, since the ignition point 11 is located approximately at the center of the combustion chamber 9, the distance from the ignition point 11 to the wall of the combustion chamber 9 is approximately uniform, and the ignited flame propagates in an approximately spherical shape without being interrupted. Since the area is larger and the flame propagation distance is shorter, the pressure rise due to combustion is faster and combustion occurs more quickly.

Furthermore, since the cooling effect from the wall surface of the combustion chamber 9 at the initial stage of propagation is small, heat loss is reduced. Furthermore, since there are fewer quench zones (lower S/V ratio), there is less unburned volume due to the quenching effect. This results in higher thermal efficiency. Furthermore, the gas flow within the combustion chamber is strengthened by the squish flow, and the flame speed increases significantly, making it possible to complete combustion in a short time.

In this way, in this embodiment, it is possible to improve combustion, and the combustion efficiency is improved, resulting in various effects such as increased output and improved fuel efficiency. Increased efficiency.

Furthermore, in this embodiment, since the combustion chamber 9 has a predetermined volume space formed by the recess 7 of the cylinder head 3 and the recess 8 of the piston 5, it is not necessary to make the recess 7 of the cylinder head 3 very deep. do not have. Therefore, the height of the cylinder head 3 is reduced, and the engine body 1 can be made more compact.

Furthermore, in this embodiment, the electrode 4 of the spark plug 4
Since a and 4b were brought to the approximate center of the combustion chamber 9,
The insertion depth of the spark plug 4 into the combustion chamber 9 becomes deeper, and the installation height of the spark plug 4 with respect to the cylinder head 3 becomes lower. From this point of view as well, the overall height of the engine body 1 can be kept low. 3
By reducing the height of the engine body 1, the engine body 1 can be made more compact, and other articles can be placed close to the engine body 1, which improves the degree of freedom in the arrangement plan.

Furthermore, in this embodiment, since a bipolar plug is used as the spark plug 4, the ignition performance is improved by strengthening the spark and doubling the chance of ignition.

Effects of the invention In the present invention, the deepest recess is formed in the cylinder head at the center of the cylinder hole top, and the deepest recess is formed in the piston at the center of the piston top to form a combustion chamber. Since the radius of curvature of the center part of the piston recess is set to be larger than the radius of curvature of the part, it is difficult to generate a component of combustion pressure that expands the piston in the radial direction. Compared to a gasket with a substantially flat top, the gasket can be obtained in a similar manner, and since the component force in the radial direction is small, the force acting on the gasket is small and blow-through is less likely to occur. Compared to the combustion chamber, the combustion chamber is structured as a spherical body, and the difference in length from the ignition point to the combustion chamber wall is smaller, improving combustion.
Since the combustion pressure itself is increasing, it is possible to increase the output.

In addition, since the ignition point of the spark plug is offset toward the cylinder head in the cylinder axial direction from the mating surface of the cylinder block and cylinder head, the flame front of the air-fuel mixture generated when ignited by the spark plug is The accompanying shock waves can be prevented from directly reaching the gasket interposed between the mating surface of the cylinder block and the cylinder head, thereby protecting the gasket from the shock waves. Since it is formed into a curved surface that gently and smoothly connects to the mating surface of the cylinder head, the combustion gas of the mixture ignited by the spark plug and causing combustion is directed to the center of the wall surface of the combustion chamber on the cylinder head side and the piston side. The flow flows smoothly from the center of the combustion chamber wall along each wall without any disturbance, and as a result, combustion can be carried out smoothly within a short time, promoting a high compression ratio of the engine and increasing the engine output. It is possible to increase fuel efficiency and improve fuel efficiency.

Furthermore, since it is formed into a smooth curve and has no sharp corners, there is no risk of post-ignition due to the sharp corners becoming heating points.

Furthermore, in the present invention, the height of the cylinder head can be lowered as described above, so the overall height of the engine can be lowered and the engine can be made more compact.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional side view showing an example of a combustion chamber of a conventional two-cycle engine, and FIG. 2 is a cross-sectional side view showing an example of a conventional engine combustion chamber.
FIG. 3 is a cross-sectional side view illustrating an embodiment of the combustion chamber structure of a two-stroke engine according to the present invention. 1... Engine body, 2... Cylinder block, 3... Cylinder head, 4... Spark plug, 5...
... Piston, 6 ... Gasket, 7, 8 ... Recess, 9 ... Combustion chamber, 10 ... Squeeze section, 11
...The ignition point.

Claims (1)

[Scope of utility model registration request] In a combustion chamber of a two-stroke engine in which a cylinder head is integrally connected to a cylinder block, the cylinder head and cylinder block have a mating surface where the cylinder head and cylinder block are integrally connected via a gasket, and the deepest part is located at the center of the top of the cylinder hole. a recess is formed in the cylinder head, and a deepest recess is formed in the piston at the center of the piston top;
A combustion chamber is configured, the radius of curvature of the central portion of the piston recess is set to be larger than the radius of curvature of the central portion of the cylinder head recess, and the ignition point of the ignition plug is set to be higher than the mating surface of the cylinder block and cylinder head. A two-cycle engine characterized in that the recesses are offset toward the cylinder head in the axial direction, and the peripheral portions of both the recesses are formed into curved surfaces that gently and smoothly connect to the mating surfaces of the cylinder block and cylinder head. Combustion chamber structure.