JP3013571B2 - Combustion chamber of a swirl chamber type diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a combustion chamber of a vortex chamber type diesel engine, and more particularly, to an improvement in a piston side cavity structure.

[0002]

2. Description of the Related Art In a swirl chamber type diesel engine, a groove-shaped trench extending from the lower part of the injection port toward the center of the piston is provided on the top surface of the piston, and a pair of large cavities is continuously formed at the tip of the trench. A configuration in which a so-called cloverleaf-type cavity is formed in a recessed manner (for example, Japanese Utility Model Laid-Open No. Sho 63-79435) is generally used. However, in this type of cavity structure, it is attempted to go straight from the injection port along the trench portion. Jet flow is too strong,
The ratio of the flame that goes over the large cavity portion and collides with the cylinder bore to extinguish the flame is relatively large, and the flame is hardly diffused in a wide area of the main combustion chamber.

Accordingly, the present applicant has previously disclosed in Japanese Patent Laid-Open No. 1-2
In Japanese Patent No. 00012, etc., a pair of substantially circular large cavities are continuously formed in a figure 8 shape on the top surface of a piston with a center line of a jet flow from an injection port interposed therebetween, and the cavity is located on the center line and near the injection port. A combustion chamber structure is proposed in which a dispersion table is raised like an island and side cavities communicating with the large cavity section are formed on both sides in front of the dispersion table.

In this apparatus, a jet jet from a vortex chamber collides with a dispersion table and diffuses into a side cavity portion, and a part of the gas whose linear velocity component is weakened by the collision crosses the dispersion table and becomes large. Since the gas flows into the cavity and generates a relatively strong swirling flow, it is possible to obtain a good air utilization rate in the main combustion chamber.

[0005]

In the conventional combustion chamber as described above, the jet is smoothly divided right and left along the outer shell on the side opposite to the injection port of the large cavity portion. , A relatively strong swirling flow can be generated. However, in the latter stage of the combustion, the swirling flows generated in each of the pair of large cavities continuous in a figure 8 shape collide with and interfere with each other.
The swirling flow is easily attenuated, and the air utilization cannot always be sufficiently increased. Therefore, there is room for further improvement in terms of suppressing unburned fuel and smoke emissions.

[0006]

According to the present invention, there is provided an injection port which is opened at a peripheral portion of a main combustion chamber and which is inclined so that a jet from a vortex chamber is directed toward the center of the main combustion chamber, and has a recess provided on a piston top surface. And, while expanding in a substantially circular shape to the left and right respectively across the center line of the jet, a pair of large cavities continuous with each other at the center, and raised near the injection port of the large cavity and on the center line A dispersion table, and a guide portion that is recessed from the vicinity of the lower part of the nozzle toward the center of the piston, and that is continuous with the large cavity portion through both sides of the dispersion table;
In a combustion chamber of a vortex chamber type diesel engine, comprising: a connection portion between a pair of large cavities; and an opposing wall portion formed as a part of the outer shell and extending toward the injection port.
It is characterized in that the curvature of the outer shell on the injection port side of the large cavity portion is made larger than the curvature on the anti-injection port side, and the tip of the outer shell near the guide portion is directed near the center of the piston.

[0007]

The combustion gas ejected from the swirl chamber near the compression top dead center through the injection port tries to go straight toward the center of the piston, and collides with the dispersion table and is divided into right and left. This flow flows into the large cavities through the guides and swirls in the large cavities. In addition, a part of the jet flowing straight over the dispersion table is split by the opposing wall, and is guided to generate a swirling flow in the large cavity. The air near the large cavity is effectively used by this swirling flow. Then, the combustion gas flowing from the outer shell on the nozzle side of the large cavity portion while swirling along the outer shell closer to the guide portion gradually turns inward, and from the tip of the outer shell closer to the guide portion described above. It flows toward the center of the piston.
Therefore, collision and interference between the pair of swirling flows are suppressed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 and 2 show a first embodiment of the present invention, in which 1 denotes a cylinder block, 2 denotes a cylinder head, and 3 denotes a piston. The lower surface of the cylinder head 2 that covers the upper surface of the cylinder bore 4 is formed as a flat surface, and the main combustion chamber 5 is formed between the lower surface and the top surface of the piston 3.

The vortex chamber 6 is located along the side of the cylinder head 2, and an injection port 7 extending from the vortex chamber 6 opens to the periphery of the main combustion chamber 5. The injection port 7 has a flat passage section with a slightly wide width direction, and is inclined so that the jet from the vortex chamber 6 is directed toward the center of the main combustion chamber 5. In FIG. 1, the center line of the above-mentioned jet on the plane of the piston 3 is indicated by a symbol L.

On the top surface of the piston 3 defining the main combustion chamber 5, a pair of large cavities 8 having a substantially circular shape are recessed at a constant depth near the center of the piston 3. The large cavity portion 8 extends right and left with the center line L interposed therebetween, and has a figure-eight shape as a whole, and central portions along the center line L are continuously integrated with each other. An outer shell 8a on the opposite side of the nozzle 7 on the center line L serving as a connection portion between the two extends in a tongue shape toward the nozzle 7;
An opposing wall 9 that partitions the two large cavities 8 is formed. The large cavity 8 also serves as a valve recess for the intake and exhaust valves.

At a position near the injection port 7 of the large cavity portion 8, there is provided a dispersion table 10 which protrudes like an island to the same height as the top surface of the piston 3. The dispersion table 10 is provided with a nozzle 7
And has a substantially rhombic planar shape so as to be positioned on the center line L so as to oppose and form a part of the outer shell of the large cavity portion 8.

At a position near the injection port 7 on the top surface of the piston 3, a side cavity portion 11 is formed to be recessed from the lower portion of the injection port 7 to the left and right along the periphery of the piston 3. The side cavity portion 11 also serves as a guide portion, has the same depth as the large cavity portion 8, and is integrally continuous with the large cavity portion 8 on both left and right sides of the dispersion table 10. The outer shell 11a of the side cavity portion 11 on the rear side of the injection port 7 has an arc shape along the periphery of the piston 3. The outer shells 11b on the left and right sides extend obliquely toward the center of the piston 3, and are provided with side cavity portions 11b.
Of the swirling flow generated in the large cavity portion 8 in a substantially tangential direction. The wall surfaces of the outer shell forming the large cavity portion 8 and the side cavity portion 11 are as follows.
The plane is perpendicular to the top surface of the piston 3.

Here, the curvature of the outer shell of the large cavity portion 8 is not uniform in each portion, and the outer shell 8c on the injection port 7 side has a larger curvature than the outer shell 8b on the opposite injection port 7 side. The distal end of the outer shell 8 d near the side cavity 11, which is the downstream end of the swirling flow, is directed near the center of the piston 3.

Next, the operation of the above embodiment will be described.

The fuel injected into the swirl chamber 6 before the compression top dead center ignites and burns in the swirl chamber 6, and becomes a flame containing unburned fuel near the compression top dead center, from the injection port 7 to the main combustion chamber 5. Spout to the side. The jet of the combustion gas first collides with the bottom surface of the central portion of the side cavity 11 where the injection port 7 faces, and an arrow a in FIG.
Diffusion to the surroundings as indicated by. The center line L from the nozzle 7
A part of the jet which is going to travel straight along the plane collides with the dispersion table 10 and diverges right and left as shown by an arrow b in FIG. Therefore, these combustion gases diffuse widely into the side cavity portion 11 and take in the surrounding air.

A part of the jet diverted to the left and right by the dispersion table 10 and the jet flowing over the dispersion table 10 flow into each large cavity 8 as shown by an arrow c, and the outer shell 8b of the large cavity 8 Turn along. Here, the above-mentioned jet flow is smoothly split right and left by the opposing wall portion 9, so that the number of flames that get over the jet wall and collide with the cylinder bore 4 is reduced, and a strong swirling flow is generated in each large cavity portion 8. You. In addition, since the jet flowing toward the side cavity portion 11 also joins from the tangential direction of the swirling flow along the outer shells 11b on the left and right sides, the swirling flow is further strengthened. Therefore, the air around the large cavity 8 is taken in widely,
The combustion spreads quickly.

The jet flow swirled in the large cavity portion 8 flows along the outer shell 8c on the injection port 7 side in the latter half of the swirl, and its direction is gradually bent inward. Finally, an arrow d is formed from the outer shell 8d near the side cavity portion 11.
Flows toward the center of the piston 3 and tries to turn again along the outer shell 8b on the side opposite to the injection port 7. Therefore, the collision between the swirling flows generated in the pair of large cavities 8, respectively,
Interference is suppressed, and the swirling flow in the large cavity portion 8 can be kept strong until the latter half of combustion.

As a result, the air utilization rate in the main combustion chamber 5 can be further increased, and the emission of unburned fuel at low load can be suppressed, and the smoke at high load can be reduced.

Next, FIGS. 3 and 4 show a second embodiment of the present invention. In this embodiment, the side cavity 11 is not provided below the nozzle 7, and the vicinity of the lower portion of the nozzle 7 and the large cavity 8 are simply formed by the groove-shaped guide 12.
Is communicated by The guide portion 12 is recessed at the same depth as the large cavity portion 8 and
The end on the side has an arc shape along the opening shape of the injection port 7,
Further, it has a planar shape that spreads in a fan shape toward the large cavity portion 8 and is continuous with the large cavity portion 8 through both sides of the dispersion table 13. Further, in this embodiment, the dispersion table 13 has an oval plane shape in which the upstream side of the jet is narrower, and the width thereof is formed smaller than the opening width of the nozzle 7. The outer shell shape of the large cavity 8 is the same as that of the first embodiment.

Therefore, in this embodiment, most of the jet flow is smoothly diverted to the left and right by the dispersion table 10 as shown by arrows in FIG. 3 and flows into the large cavity portion 8 from a substantially tangential direction. For this reason, a stronger swirling flow is generated in the large cavity 8, and diffusion combustion can be performed around the large cavity 8. This strong swirling flow can be maintained until the latter half of combustion.

[0022]

As is apparent from the above description, according to the combustion chamber of the swirl chamber type diesel engine according to the present invention, the flow of the combustion gas swirling in the large cavity portion gradually turns inward in the latter half of the swirl. And the swirling flows generated in the pair of large cavities continuous in a figure 8 shape do not collide with each other and interfere with each other, and the attenuation is suppressed. Is done. That is, the swirl flow is strongly maintained until the latter half of the combustion in the main combustion chamber, so that the air utilization rate can be further increased, and the emission of unburned fuel at low load can be suppressed and the smoke at high load can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan view of a piston top surface showing a first embodiment of a combustion chamber according to the present invention.

FIG. 2 is a cross-sectional view of a main part of the combustion chamber along the line AA in FIG. 1;

FIG. 3 is a plan view of a piston top surface showing a second embodiment of the combustion chamber according to the present invention.

FIG. 4 is a cross-sectional view of a main part of the combustion chamber taken along line BB in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 3 ... Piston 5 ... Main combustion chamber 6 ... Swirl chamber 7 ... Injector 8 ... Large cavity part 9 ... Opposing wall part 10 ... Dispersion table 11 ... Side cavity part (guide part) 12 ... Guide part 13 ... Dispersion table

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F02B 19/08-19/18 F02F 3/26-3/28

Claims (1)

(57) [Claims] 1. An injection opening which is open to a peripheral portion of a main combustion chamber and is inclined so that a jet from the vortex flow chamber is directed toward a center of the main combustion chamber, and a recess provided on a piston top surface and a center line of the jet. A pair of large cavities, which are substantially circular to the left and right, and are continuous with each other at the center, and a dispersion table raised near the nozzle of the large cavity and on the center line, from near the lower part of the nozzle A guide portion recessed toward the center of the piston and connected to the large cavity portion through both sides of the dispersion table, and a connecting portion between the pair of large cavity portions, formed as a part of the outer shell thereof, and a nozzle; And a facing wall extending toward the vortex chamber type diesel engine, wherein the curvature of the outer shell on the injection port side of the large cavity portion is larger than the curvature on the anti-injection port side, and the guide section. The tip of the outer shell A combustion chamber for a vortex-chamber diesel engine, the end of which is oriented near the center of the piston.