JPH0119050B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a pent roof-shaped combustion chamber structure in an engine having two intake ports and one exhaust port each independently opening into the combustion chamber. It is.

(Prior art) Conventionally, for example, as shown in Japanese Patent Application Laid-Open No. 56-44419, a three-way engine has been developed, in which a primary port, a secondary port, and an exhaust port are opened in the combustion chamber of an engine.
In a valve-type engine, a guide wall that protrudes into the combustion chamber is provided along a part of the outer periphery of the primary port, and this guide wall causes the intake air introduced from the primary port into the combustion chamber to swirl in the circumferential direction of the combustion chamber. Combustion chamber structures designed to strengthen the combustion chamber are known. In the above combustion chamber structure, in low speed or low load ranges, intake air is introduced only from the primary port to improve the intake air flow velocity, and the swirl is strengthened by the guide wall, promoting vaporization and atomization of the fuel and increasing the combustion rate. At the same time, intake air is also introduced from the secondary port at high speed or high load ranges to improve output.

Furthermore, a pent roof shape is known as a combustion chamber shape of an engine, in which the wall surface of the cylinder head is formed by two inclined surfaces that are inclined around a ridgeline. However, when the above-described two intake ports and exhaust ports are arranged in the pent-roof-shaped combustion chamber and a swirl is generated by the guide wall, when the intake air amount increases, It is preferable to prevent the guide wall from becoming an obstacle to the flow of intake air and increasing intake resistance.

Furthermore, there is also a known technique in which the bottom surface of the cylinder head protrudes into the cylinder bore to generate a squishing flow as the piston rises to improve the combustion rate (for example, see Japanese Patent Application Laid-Open No. 57-203818). When trying to generate a squish flow in a pent roof-shaped combustion chamber as described above, if the direction of the squish flow is not set with consideration to the direction of the swirl, the two flows will interfere and a sufficient effect will not be obtained. It disappears. In other words, in a pent roof-shaped combustion chamber, the distance between the combustion chamber head wall surface and the piston head surface is different between the ridgeline part and the part far from the ridgeline near the top dead center of the piston, and there are two intake ports, an exhaust port, and an ignition port. If the arrangement relationship with the plug and the generation of the swirl and squishy flow are not taken into consideration as a whole, the squishy flow will simply be formed by the bottom surface of the protrusion that has a guide wall formed to generate the swirl. In some cases, the generated squish flow may weaken the swirl, and the flammability has not been sufficiently improved in the entire combustion chamber, including the area near the secondary port, which is far from the spark plug and has low flammability. There is no problem.

(Object of the Invention) In view of the above circumstances, the present invention utilizes the characteristics when two intake ports and one exhaust port are arranged in a pent roof-shaped combustion chamber, and increases intake resistance by a swirl port. A combustion chamber for an engine that generates swirl without weakening the swirl, synchronizes the squish flow without weakening the swirl, and grows the flame toward the secondary port side, thereby improving combustibility throughout the combustion chamber. The purpose is to provide structure.

(Structure of the Invention) The combustion chamber structure of the engine of the present invention is such that the combustion chamber has a pent-roof shape with two sloped surfaces centered around a ridgeline, and one sloped surface has two slanted surfaces substantially parallel to the ridgeline direction.
Two intake ports are opened, and an exhaust port and a plug hole are opened on the other inclined surface. One of the intake ports is a swirl port that introduces intake air in a direction approximately tangential to the cylinder bore, while the other intake port is used for low speed or The secondary port is used to suppress intake air in the low load range, and the exhaust port is located at a position that is almost opposite to the secondary port with respect to the ridgeline, and the plug hole is located at a position that is approximately opposite to the swirl port with respect to the ridgeline. Furthermore, along the cylinder bore on the back side of the plug hole, a protrusion that protrudes toward the center of the cylinder bore from near the swirl port to near the exhaust port is provided on the wall surface of the cylinder head, and the side surface of the protrusion toward the center of the cylinder bore is aligned approximately with the direction of piston movement. The curved surface is parallel and bulges toward the outer circumferential direction of the cylinder bore, and both ends of the curved surface in the circumferential direction of the cylinder bore are smoothly connected in the tangential direction of the cylinder bore, forming a guide surface that smoothly guides the intake air from the primary port in the tangential direction of the cylinder bore. However, the lower surface of the protrusion is characterized in that it is a squishing area that generates squishing flow in a direction that promotes swirl when the piston rises.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.
In the engine shown in FIGS. 1 and 2, 1
2 is a cylinder block, 2 is a cylinder head, 3 is a piston, and 4 is a combustion chamber formed by cylinder block 1, cylinder head 2, and piston 3.

5 indicates a swirl port by one intake port opening into the combustion chamber, 6 indicates a secondary port by the other intake port, 7 indicates an exhaust port for exhaust,
The swirl port 5 connects to a primary intake passage 8 that opens to one side of the cylinder head 2, the secondary port 6 connects to a secondary intake passage 9 that also opens to one side of the cylinder head 2, and the exhaust port 7 connects to the other side of the cylinder head 2. Each of them communicates with an exhaust passage 10 that opens on the side.

The swirl port 5, the secondary port 6, and the exhaust port 7 have a primary intake valve 11, a secondary intake valve 12, and an exhaust valve 13 seated on their respective valve seats.
is installed.

Further, reference numeral 14 denotes a plug hole into which an ignition plug is attached, and is opened so that the electrode portion of the ignition plug faces directly downstream of the swirl port 5 of the combustion chamber 4 in the inflow direction.

The shape of the combustion chamber 4, that is, the cylinder head 2
The shape of the bottom wall surface is shown by contour lines in Figure 3, and
As shown in the cross section in Fig. 5, the center line parallel to the side surface of the cylinder head 2 is the ridge line (deepest part).
It is provided in a chevron-shaped pent roof shape with two slopes inclined on both sides around this ridgeline, and two intake ports, that is, swirl ports 5 and 5 are provided on one sloped surface of this pentroof shape substantially parallel to the direction of the ridgeline. Secondary port 6 opens. Further, an exhaust port 7 is opened on the other inclined surface at a position substantially opposite to the secondary port 6 with respect to the ridgeline, and a plug hole 14 (ignition plug) is opened at a position substantially opposite to the swirl port 5 with respect to the ridgeline. )
is installed. In the pent roof-shaped combustion chamber 4 as described above, near the top dead center of the piston 3, the distance between the combustion chamber head wall surface and the piston head surface differs between the ridgeline and the portion far from the ridgeline.

The swirl port 5 opens at a position offset from the center of the combustion chamber 4 when viewed in plan, and is provided so as to introduce intake air from a substantially tangential direction of the cylinder bore C (outer diameter of the piston 3) to generate a swirl A. It is being The primary intake passage 8 connected to the swirl port 5 has a downstream portion thereof curved outward when viewed from above, so that the intake flowing down the primary intake passage 8 often covers the outside of the stem 11a of the primary intake valve 11. The flow flows from the swirl port 5 to the outer circumferential side of the cylinder bore C to increase the generation of swirl A, and the inclination angle is set small so that the inflow angle on the vertical cross section is as close to horizontal as possible. The intake air flows toward the air, making swirl A more reliable.

On the other hand, the secondary intake passage 9 connected to the secondary port 6 is set to have a larger inclination angle than the primary intake passage 8 so as to allow intake air to flow in along the cylinder bore axis direction in a vertical section. Reference numeral 6 is formed at a so-called output port to introduce intake air while suppressing the generation of swirl, and the introduction of intake air is suppressed in a low speed or low load range.

Further, reference numeral 15 indicates a valve operating mechanism that opens and closes the primary intake valve 11, secondary intake valve 12, and exhaust valve 13 at predetermined timing.
8, etc., and is provided with a valve deactivation device 19 that disables the opening/closing operation of the secondary intake valve 12. This valve deactivation device 19
The fulcrum position of the hydraulic tappet 18 constituting the swing fulcrum of the shaft is raised and lowered by the operating cam 20. When the valve deactivation device 19 is activated, the rocker arm 17 moves the secondary intake valve 12 against the movement of the shaft 16. The secondary intake valve 12 is held in an open state by a valve spring 21.

Figure 6 shows the primary intake valve 11 and the secondary intake valve 12.
and the opening/closing timing of the swirl port 5, secondary port 6, and exhaust port 7 by the exhaust valve 13. The exhaust port 7 opens near the bottom dead center in the latter half of the explosion stroke and closes near the top dead center.
On the other hand, swirl port 5 (primary port) opens before and after the exhaust port closes near top dead center, closes near bottom dead center in the latter half of the intake stroke, and secondary port 6 opens earlier and later than swirl port 5. The secondary port 6 is set to close, and the opening area in the fully closed state is larger than the small diameter swirl port 5.
is larger.

Further, the valve deactivation device 19 is activated according to the engine speed and torque (load), and as shown in FIG. The intake valve 12 is maintained in a closed state, and the primary intake valve 1 is provided in the combustion chamber 4.
Intake air from the primary intake passage 8 is supplied only from the swirl port 5 opened by the valve 1, while the valve deactivation device 19 does not operate in the high rotation (high load) region and the secondary intake valve 12 is operated by the camshaft 16. The secondary port 6 opens and closes according to the movement, and in addition to introducing the intake air from the swirl port 5, the secondary intake passage 9 supplies intake air to the combustion chamber 4. In addition, the reason why the boundary line D of the switching region in FIG. 7 is set to be inclined with respect to the rotation speed is because even when the engine speed is high, the amount of intake air is small in the low torque (load) region, so the swirl This is because a sufficient amount of intake air can be secured by supplying only through port 5.

On the other hand, in the pent roof-shaped combustion chamber 4,
With the opening of each port 5, 6, 7 and the plug hole 14, a space is created on the back of the plug hole 14, and a part of the wall surface of the cylinder head 2 along the cylinder bore C on the back of the plug hole 14 is From near swirl port 5 to exhaust port 7
A protrusion 22 that protrudes toward the center of the cylinder bore C is formed near the center of the cylinder bore C. The lower surface 22a of the protruding portion 22 is configured as a squishing area that generates squishing flow B that causes the combustion gas ignited by the spark plug to flow toward the opposite side (towards the center) of the cylinder bore when the piston 3 rises. The amount of protrusion of the protruding portion 22 gradually increases from near the ridgeline of the pent roof shape, that is, near the swirl port 5, to a predetermined position on the downstream side in the flow direction of the swirl A, reaches the maximum at the back of the plug hole 14, and extends toward the exhaust port 7. It is formed so that it gradually decreases.

Further, the side surface of the protrusion 22 is formed into a curved guide surface 22b that smoothly guides the intake air from the swirl port 5 in the tangential direction of the cylinder bore C.

That is, the guide surface 22b is a curved surface that is substantially parallel to the direction of piston movement and bulges toward the outer circumferential direction of the cylinder bore, and is formed so that both ends of the curved surface in the circumferential direction of the cylinder bore are smoothly connected in the tangential direction of the cylinder bore. .

In addition, the squishing area that forms the squishing flow B, that is, the angle of inclination from the lower surface 22a of the protrusion 22 to the guide surface 22b is on the swirl port 5 side (the right side in FIG. 4) near the ridgeline (center line) of the combustion chamber 4. The angle is steep in some parts, whereas the angle is gentler in the part on the exhaust port 7 side (left side in FIG. 5) as it moves away from the ridgeline. Therefore, the squishing flow B in each part of the protrusion 22 heads toward the secondary port 6 on the opposite side of the cylinder bore, but its strength varies in magnitude, and in the steep angle part near the ridgeline on the swirl port 5 side, the squishing flow B When the flow exits from the lower surface 22a, it disperses and becomes weaker, while at the gentle angle part of the exhaust port 7 side in the downstream direction of the swirl A, there is less dispersion when exiting from the lower surface 22a, and the squish flow B becomes stronger, and as a whole, The squish flow B tends toward the exhaust port 7 side, and is generated so as to back up in sync with the swirl A caused by the swirl port 5 without weakening it.

In addition, on the wall surface of the cylinder head 2, there are auxiliary protrusions 23 and auxiliary protrusions 23 that protrude outwardly between the swirl port 5 and the secondary port 6 and between the secondary port 6 and the exhaust port 7, respectively, and inwardly of the cylinder bore C. 24 is formed. This auxiliary protrusion 23,2
4 also forms a squish flow, but this is relatively weak and does not disturb the large intake flow; rather, the formation of the auxiliary protrusions 23 and 24 reduces the dead volume of the combustion chamber 4. This has the effect of reducing the amount of residual unburned gas.

Further, a plug hole 14 for attaching a spark plug is provided near the protrusion 22, and a plug hole 14 is provided near the protrusion 22.
The squish flow B caused by 2 directly acts on the electrode portion of the spark plug and scavenges this electrode portion together with the swirl A, so that the ignition performance is improved.

In the above configuration, the secondary intake valve 12 is closed by the valve deactivation device 19 when the intake air amount is small at low speeds or in a low load range.
Intake air is supplied to the combustion chamber 4 only from the swirl port 5 while generating a swirl A, and this intake swirl A is smoothly guided in the tangential direction of the cylinder bore C by the guide surface 22b of the protrusion 22, and the ignition plug immediately downstream It curves in the direction of the exhaust port 7 through the vicinity and flows into the secondary port 6, forming a spiral swirl A as a whole. Further, as the piston 3 rises, a squishing flow B is generated in synchronization with the swirl A by the squishing area of the lower surface 22a of the protrusion 22, and the intake air is ignited by the spark plug before the top dead center. Then, the flame ignited by the spark plug is pushed toward the center of the cylinder bore C by the squish flow B, promoting the growth of the flame in the direction of the secondary port 6, and causing the flame to grow at a position away from the spark plug. The combustion rate has been improved,
Combustion performance is improved and torque increases.

Furthermore, when the amount of intake air is large at high speed or in a high load range, intake air is supplied from the secondary port 6 in addition to the swirl port 5, and the formation of swirl in the intake air supplied from the secondary port 6 is suppressed. , the intake air filling efficiency is improved and high output can be obtained.

That is, as shown in the full-open curve shown in FIG. 7, when the secondary intake valve 12 is closed at low rotation speeds and the intake air is taken only by the swirl port 5, the intake air is supplied with a high flow rate of swirl A and the squishy flow B.
The generation of combustibility improves and large torque can be obtained, but the intake air amount increases as the rotation speed increases, and the torque decreases due to insufficient air intake due to the narrow passage area. The torque decreases after exceeding the peak, but at this time the secondary intake valve 12 is opened and intake air starts being supplied from the secondary port 6, and the torque increases, resulting in good torque characteristics over the entire operating range. It will be done.

The supply of intake air from the secondary port 6 is controlled not only by the valve deactivation device 19 but also by an on-off valve 25 in the middle of the secondary intake passage 9, as shown by the imaginary line in FIG. Similarly to the operation of the valve deactivation device 19, the on-off valve 25 may be opened and closed in a low speed or low load range to obtain the switching characteristics shown in FIG. In addition, this switching characteristic may be performed mainly depending on the engine speed as shown in Fig. 7, or it may be performed mainly depending on the engine load fluctuation. The intake air is supplied only through the swirl port 5 to improve the flow velocity, and when the intake air amount increases, the intake air is also supplied from the secondary port 6 to increase the filling amount and improve the output.

(Effects of the Invention) According to the present invention as described above, the unique characteristics of a pent roof-shaped combustion chamber, that is, the height of the combustion chamber is different between the ridgeline part and the peripheral part, and a swirl port and two When the secondary port is opened, the exhaust port is opened on the other inclined surface at a position almost opposite to the secondary port, and the plug hole is opened at a position almost opposite to the swirl port, a space is created on the back side of the plug hole. Focusing on
A protrusion that gradually increases in protrusion from the vicinity of the ridgeline toward the downstream side in the swirl direction is formed in a specific area on the back of the plug hole where there is plenty of space, and the bottom surface of this protrusion forms a squeezing area. By doing so, it is possible to generate a squishing flow by the squishing area in a certain circumferential direction, synchronize the direction of the swirl generated by the swirl port with the squishing flow, and strengthen the squishing flow and the swirl. Creates an airflow that
The flame ignited by the spark plug adjacent to the combustion area can be effectively propagated to the vicinity of the secondary port, which becomes the end gas zone, thereby improving the combustibility of the combustion complete body.

[Brief explanation of drawings]

Fig. 1 is a vertical sectional view of the main parts of an engine according to an embodiment of the present invention, Fig. 2 is a bottom view of the cylinder head, Fig. 3 is a bottom view showing the shape of the combustion chamber of the cylinder head along with contour lines, and Fig. 4 is a bottom view of the cylinder head. Figure 3 -
Figure 5 is a cross-sectional view taken along the - line in Figure 3, Figure 6 is a curve diagram showing the opening/closing timing of each port, and Figure 7 shows the switching area between the swirl port and the secondary port. It is a characteristic diagram shown together with a fully open curve. 1... Cylinder block, 2... Cylinder head, 3... Piston, 4... Combustion chamber, 5... Swirl port, 6... Secondary port, 7... Exhaust port, 11... Primary intake valve, 12 ...Secondary intake valve,
13...Exhaust valve, 14...Plug hole, 22...
...protrusion, 22a...bottom surface (squeeze area),
22b... Guide surface, 25... Opening/closing valve, A... Swirl, B... Squeeze flow, C... Cylinder bore.

Claims (1)

[Claims] 1. The wall surface of the cylinder head that forms the combustion chamber is shaped like a pent roof with two inclined surfaces that are inclined around the ridge line, and two intake ports are opened on one of the inclined surfaces in approximately parallel to the direction of the ridge line, and the other inclined surface is In an engine that has an exhaust port and a plug hole where a spark plug is attached to the surface, one of the intake ports is a swirl port that introduces intake air approximately tangentially to the cylinder bore, while the other intake port is used for low speed or low load operation. The secondary port is such that the introduction of intake air is suppressed in the area, and the exhaust port is located at a position substantially opposite to the secondary port with respect to the ridgeline, while the plug hole is located approximately opposite to the swirl port with respect to the ridgeline. At the same time, along the cylinder bore on the back side of the plug hole, a protrusion is provided on the wall surface of the cylinder head that protrudes toward the center of the cylinder bore from near the swirl port to near the exhaust port. The side surface is a curved surface that is almost parallel to the direction of piston movement and bulges toward the outer circumferential direction of the cylinder bore, and both ends of the curved surface in the circumferential direction of the cylinder bore are formed to smoothly connect in the tangential direction of the cylinder bore, thereby directing intake air from the primary port to the cylinder bore. A combustion chamber structure for an engine, characterized in that it has a guide surface that guides smoothly in the tangential direction, and a lower surface of the protrusion is a skid area that is close to the piston head surface when the piston is at the top dead center.