JPS6250647B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cylinder head for an internal combustion engine with two spherical combustion chambers.

[Conventional technology]

In a four-stroke reciprocating engine, in order to improve its output, it is conceivable to improve the flow of intake and exhaust air in the combustion chamber. For example, by creating a hemispherical combustion chamber, not only can the diameters of the intake and exhaust valves be increased and intake and exhaust resistance can be reduced, but also the connection between the intake and exhaust holes and the inside of the combustion chamber is smooth, allowing for smooth intake and exhaust flow. The flow will be better and output performance can be expected to improve. However, in the case of such a hemispherical combustion chamber, the hemisphere of the cylinder head and the cylinder are formed in a smooth continuity, so the piston
There is no area (squeeze area) sandwiched between the peripheral edge of the head and the cylinder head, and compression turbulence (squeeze) does not occur. This results in a disadvantage that the fire propagation speed becomes low and the required octane number for stable operation of the engine becomes high.

Therefore, for example, Japanese Patent Application Publication No. 51-64111, Utility Model Application No. 53
A two-spherical combustion chamber in which the combustion chamber was formed of two domes (spherical shapes) as shown in Publication No. 58202 was considered. In the case of two spheres, the opening formed when each dome intersects the combustion chamber mating surface becomes approximately Daruma-shaped, so a step is formed between the circumference of this opening and the cylinder, and this step and the piston. The intake air is caught between the head and the head, creating compression turbulence. This increases the fire propagation speed, promotes combustion, enables stable operation, and lowers the required octane number.
Further, by forming the two-spherical combustion chamber, the volume of the combustion chamber can be reduced, so that it is possible to increase the compression ratio and increase the output accordingly.

In addition, in this invention, in order to smoothly match the bore size of the cylinder, the approximately daruma-shaped opening formed in each dome intersects the joint surface of the cylinder head and cylinder block, that is, the joint surface of the combustion chamber. A combustion chamber in which the outer periphery of the Daruma-shaped opening is chamfered conically or spherically is also considered to be a bispherical combustion chamber.

In such a two-spherical combustion chamber, in the conventional one, the exhaust side dome where the exhaust valve is provided and the intake side dome where the intake valve is installed are approximately the same, or the exhaust side dome is smaller than the intake side dome. It is formed like this. This is because intake and exhaust valves are generally made to be larger than the valve head diameter of the intake valve due to differences in gas flow velocity, etc., but the diameter of each dome was determined according to the valve head diameter of the intake valve. In addition, the dome radius on the intake valve side, where the valve umbrella diameter is large, is formed to be large.

[Problem that the invention seeks to solve]

However, such a two-spherical combustion chamber in which the exhaust side dome and the intake side dome are approximately the same or the intake side dome is larger has the disadvantage that the flow coefficients of the intake hole and the exhaust hole are poor. Figures 1 and 2 show the intake and exhaust valve lift amounts, respectively.
It is a graph which shows an example of the change characteristic of an exhaust hole flow coefficient. In this graph, the flow coefficient is determined by keeping the pressure difference between the upstream and downstream sides of the intake and exhaust valves constant.
It is calculated based on the flow rate of steady flow passing through the intake and exhaust holes, and the larger the value of this flow rate coefficient, the greater the gas flow rate per unit valve area.
In these figures, symbols a and b indicate characteristics in a conventional two-spherical combustion chamber. In particular, as shown in FIG. 2, in the conventional type with a relatively small exhaust side dome, the rate of increase in the exhaust hole flow coefficient decreases as the exhaust valve lift increases.

[Means for solving problems]

This invention was made in view of the above-mentioned disadvantages, and by forming the intake side dome smaller than the exhaust side dome, the intersection line formed by both domes on the wall surface of the combustion chamber is aligned with the opening edge of the combustion chamber. The dome is curved in a direction that moves away from the exhaust hole as it approaches the exhaust hole, and a stepped portion is formed between the opening edge of the intake side dome and the inner circumferential surface of the cylinder.

[Effect]

During the intake stroke, there is an intersection line (ridge line) formed by both domes on the downstream side of the intake hole in the combustion chamber wall near the intake hole, and an intersection line formed between the opening edge of the intake side dome and the cylinder inner peripheral surface. The stepped portion artificially causes separation due to separation of the boundary layer, and in the exhaust stroke, the smooth wide surface of the exhaust side dome, which is the upstream side of the exhaust hole, provides a smooth flow.

〔Example〕

FIG. 3 is a partially sectional side view of a twin overhead camshaft gasoline engine to which an embodiment of the present invention is applied;
FIG. 4 is a vertical front view, and FIGS. 5A and 5B are a vertical side view and a bottom view of the cylinder head showing the two-spherical combustion chamber shape. In Figs. 3 and 4, reference numeral 1 is a crank case, 2 is a cylinder block, and 3 is a cylinder head. A cylinder liner 4 is fitted into the cylinder block 2 and fixed by the cylinder head 3. ing. The cylinder liner 4 is pressed at the joint surface 5 of the cylinder block 2 and cylinder head 3, that is, the combustion chamber joint surface 5. 6 is a piston that slides inside this cylinder liner 4, and 7 is the above-mentioned crank.
A crankshaft 8 held within the case 1 is a connecting rod that connects the piston 6 and the crankshaft 7. The cylinder head 3 is provided with a recess corresponding to the cylinder liner 4, in which a two-spherical combustion chamber 9 is formed. This combustion chamber 9 includes an umbrella portion 10a of an intake valve 10, and an umbrella portion 10a of an intake valve 10.
The umbrella portion 11a of the exhaust valve 11, which has a diameter smaller than that of a, faces and partitions the combustion chamber 9 from the intake passage 12, the exhaust passage 13, and the combustion chamber 9, respectively. The intake valve 10 and the exhaust valve 11 move in synchronization with the rotation of the crankshaft 7 by a known valve mechanism including camshafts 14, 15, a tappet 16, etc., and are connected to an intake hole 17 and an exhaust hole 18, respectively. Open and close. In FIG. 3, 19 is a carburetor connected to the upstream side of the intake passage 12, and 20 is an exhaust pipe connected to the downstream side of the exhaust passage 13. Further, in FIG. 4, 21 is a spark plug.

Next, the shape of the two-spherical combustion chamber 9 will be explained based on FIG. 5. Figure A is a longitudinal sectional side view of the cylinder head 3, Figure B is its bottom view, and the intake valve 10 is
is provided on the intake side dome 22, and the exhaust valve 11 is provided on the intake side dome 22.
is provided on the exhaust side dome 23. The radius R ₁ of the exhaust side dome 23 is the radius R ₂ of the intake side dome 22
The domes 22 and 23 intersect with each other, and the line of intersection 24 passes between the intake valve 10 and the exhaust valve 11. And each of these domes 22,2
In the substantially daruma-shaped opening 25 as shown in _FIG .
larger than the aperture radius r ₂ of 2. Therefore, in this Daruma-shaped opening 25, the exhaust side dome 2
3 is larger than the area occupied by the intake side dome 22, and the intersection line (ridge line) 2 formed by both domes 22 and 23 on the upper wall surface of the combustion chamber 9.
4 is an exhaust hole 18 as it approaches the opening 25.
It curves in the direction away from. In FIG. 5, 26 represents the inner circumferential surface of the cylinder liner 4. As shown in FIG. As is clear from the figure, a step 27 is formed between the outer periphery of the opening 25 and the cylinder liner 4. That is, in the intake side dome 22, the distance from the opening edge of the intake hole 17 to the intersection line 24 and the opening line 25a of the intake side dome is made as short as possible. Therefore, there is no particular reason why the intake side dome 22 necessarily has to be hemispherical, and it may have a shape similar to this as long as the above conditions are met. Note that although this stepped portion 27 is formed with a spherical chamfer in FIG. 4 to promote gas flow, this spherical chamfer is not shown in FIG. 5A. Further, in FIG. 5B, 28 is a mounting hole for the ignition plug 21.

In the engine configured as described above, during the intake stroke in which the piston 6 descends, the intake valve 10 is opened by the valve operating mechanism, and the intake air passes through the carburetor 19, the intake passage 12, and the intake hole 17, and is combusted. is inhaled into chamber 9. At this time, the intake air passes between the umbrella part 10a and the intake hole 17 along the back surface (the surface on the intake passage 12 side) of the umbrella part 10a of the intake valve 10, and then flows into the combustion chamber 9 along the intake side dome 22. flows into. The flow coefficient characteristics at this time are shown in FIG. 1A. That is,
By making the radius R ₂ of the intake side dome 22 smaller than that of the conventional combustion chamber, the wall surface on the downstream side of the intersection line 24 and the opening edge 25a of the intake side dome 22 is pushed back with respect to the flow direction. By causing the boundary layer to separate, the substantial flow path space is prevented from narrowing and the flow coefficient characteristics are improved.

After passing through a compression stroke and an explosion stroke, the exhaust valve 11 opens when the engine enters an exhaust stroke, and as the piston 6 moves upward, burned gas is guided to the exhaust passage 13 and the exhaust pipe 20. At this time, the gas is guided to the exhaust side dome 23 of the combustion chamber 9 and the umbrella portion 1 of the exhaust valve 11
1a and the exhaust hole 18, and flows along the back surface of the exhaust valve 11 (the surface on the exhaust passage 13 side).
Exhaust side dome 2 occupying the Daruma-shaped opening 25
Since the cylinder head 3 is configured to have a smooth curved surface and a large area, more of the gas that comes into contact with the cylinder head 3 comes into contact with the exhaust side dome 23. Therefore, more gas is guided along the exhaust side dome 23 than in the case of a conventional combustion chamber shape, so that the gas can be smoothly exhausted. B in FIG. 2 represents the flow coefficient characteristic of this embodiment, and it is clear from the results that the performance is significantly improved compared to characteristic b of the conventional combustion chamber shape.

In addition, in the compression stroke, at the end of the stroke, the stepped portion 27 on the outer periphery of the Daruma-shaped opening 25
Since the intake gas is trapped between the combustion chamber 9 and the piston head of the piston 6, this gas is pushed toward the center of the combustion chamber 9, and the gas turbulence becomes intense (compression turbulence). As a result, the fire propagation speed increases, knocking etc. are less likely to occur, and operation becomes stable.

〔Effect of the invention〕

As explained above, according to the present invention, by forming the intake side dome smaller than the exhaust side dome, the line of intersection formed by both domes on the wall surface of the combustion chamber is adjusted closer to the opening edge. It is curved in a direction away from the hole, and a stepped portion is formed between the opening edge of the intake side dome and the inner peripheral surface of the cylinder. Therefore, during the intake stroke, the boundary layer is created near the intake valve by the intersection line formed by both domes and the step formed between the opening edge of the intake side dome and the inner peripheral surface of the cylinder. Since separation occurs due to peeling, the flow path is not narrowed due to boundary layer peeling unlike in conventional intake side domes, and the flow coefficient can be improved. In addition, in the exhaust stroke, the opening area of the exhaust side dome in the approximately Daruma-shaped opening becomes relatively large, so the flow of burned gas becomes smoother and the flow coefficient is improved, so exhaust is promoted and inside the combustion chamber. The amount of residual gas remaining is reduced. Therefore, the improvement in the flow coefficient on the intake valve side improves the volumetric efficiency (intake efficiency), which greatly contributes to an increase in engine output.

[Brief explanation of the drawing]

1 and 2 are graphs showing flow coefficient characteristics of intake holes and exhaust holes, respectively, and FIG. 3 is a partially sectional side view of an internal combustion engine showing an embodiment of the present invention.
FIG. 4 is a vertical front view, and FIGS. 5A and 5B are a vertical side view and a bottom view of the cylinder head showing the two-spherical combustion chamber shape which is the essential part of the present invention. 3... Cylinder head, 5... Combustion chamber mating surface,
9...2 spherical combustion chambers, 10...intake valve, 11...
Exhaust valve, 22... Intake side dome, 23... Exhaust side dome, 25... Daruma-shaped opening, R ₁ ... Exhaust side dome radius, R ₂ ... Intake side dome radius, r ₁ ...
Opening radius of the exhaust side dome, r ₂ ... Opening radius of the intake side dome.

Claims (1)

[Claims] 1. In an internal combustion engine equipped with two spherical combustion chambers 9 formed by an intake side dome 22 provided with an intake valve 10 and an exhaust side dome 23 provided with an exhaust valve 11, the intake side dome 22 is By forming the dome smaller than the exhaust side dome 23, the intersection line 24 formed by both domes 22 and 23 on the wall surface of the combustion chamber is directed in a direction that moves away from the exhaust hole 18 as it gets closer to the opening edge 25 of the combustion chamber 9. curved into
A cylinder head for an internal combustion engine, characterized in that a stepped portion 27 is formed between an opening edge 25a of an intake side dome 22 and a cylinder inner peripheral surface 26.