JP3013573B2 - 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 initially jetted from the vortex chamber collides with the dispersion table and diffuses into the side cavity, and a part of the gas whose straight-running velocity component is weakened by the collision crosses the dispersion table. And flows into the large cavity portion, where a swirling flow is generated. Also, with the lowering of the piston, most of the jet flows over the dispersion table and flows into the large cavity, but at this stage, since the straight traveling speed component is weak, the swirling flow also follows the inner circumference of the large cavity. Raise it. Therefore, it is possible to obtain a good air utilization rate in the main combustion chamber.

[0005]

In the combustion chamber structure in which the dispersion table is provided so as to close the path of the jet as described above, the jet is diffused widely in the side cavities, but is generated in the large cavity. The swirling flow is not always sufficiently strong, and the air utilization near the large cavity cannot 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 a pair of large cavities which are substantially circularly spread left and right with respect to the center line of the jet, respectively, and which are continuous with each other at the center, and a groove which is narrower than the opening width of the nozzle and deeper than the large cavity. A guide groove extending from the lower part of the injection port along the jet flow center line, the tip end side being formed gradually shallower, and a bifurcated tip part connected to each large cavity part from the circumferential direction. A pair of dispersion tables that form part of the outer shell on the nozzle side of the large cavity portion and that protrude so as to sandwich the guide groove from both sides; From below the nozzle A passage portion that is continuous with the large cavity portion through the side of the dispersion table, and a connecting portion between the pair of large cavity portions, an opposing wall portion that is formed as a part of the outer shell and extends toward the injection port; It is characterized by having.

[0007]

The combustion gas ejected from the swirl chamber through the injection hole near the compression top dead center tends to go straight toward the center of the piston. A part of this jet collides with the dispersion table and is widely dispersed around. A part of the jet flows straight along the guide groove and flows into the left and right large cavities from the bifurcated tip from the circumferential direction. As a result, a strong swirling flow is generated in the large cavity portion, and the air in the vicinity thereof is effectively used. The jet colliding with the dispersion table and dispersed merges with the swirling flow through the passage to further activate the gas flow in the large cavity.

[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. The outer shell on the center line L on the side opposite to the injection port 7 serving as a connection portion extends in a tongue shape toward the injection port 7 to the vicinity of the center of the piston 3, and opposes the two large cavity portions 8. A part 9 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 8, a pair of dispersion tables 10 are provided which are raised in an island shape to the same height as the top surface of the piston 3. This dispersion table 10
Are arranged symmetrically with respect to the jet center line L. The arc-shaped wall surface 10a on the side of the large cavity 8 forms a part of the outer shell of the large cavity 8, and the nozzle The wall surface 10b on the side of the nozzle 7 is linearly formed substantially along the front edge of the opening of the nozzle 7. Furthermore, the left and right side walls 10c
Are inclined toward the center of each large cavity portion 8.

The passage portion 11 has the same depth as the large cavity portion 8 so as to surround the pair of dispersion tables 10.
Is recessed. The passage portion 11 has a loose arc shape so that the lower portion of the injection port 7 is along the outer periphery of the piston 3, and is formed in a groove shape from both ends toward the center of each large cavity portion 8. In other words, it is continuous with the large cavity portion 8 from the substantially radial direction through the side of the dispersion table 10.
The wall surface of the outer shell forming the large cavity 8 and the passage 11 is perpendicular to the top surface of the cylinder 3.

On the top surface of the piston 3, a guide groove 12 is formed deeper than the large cavity portion 8. A base end 12 a of the guide groove 12 is located below the injection port 7 of the passage portion 11 and extends along the jet center line L so as to be sandwiched between the pair of dispersion tables 10 therefrom. And piston 3
The front end portion 12b near the center is branched in a forked shape, and is connected to each large cavity portion 8 from the circumferential direction. The guide groove 12 has a width of about 1/3 of the opening width of the injection port 7 and, as shown in FIG. I have.

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 basically goes straight along the jet center line L, and a part of the jet collides with the dispersion table 10 and diffuses around. Thus, the initial combustion on the main combustion chamber 5 side starts immediately.

A part of the jet flows straight along the guide groove 12 passing between the pair of dispersing tables 10 and flows into the large cavity 8 from the circumferential direction along the forked tip 12b. Also, a component that is supposed to go straight through the guide groove 12 is diverted smoothly to the left and right by the opposing wall portion 9. Therefore, as shown by the arrow a in FIG. 1, a very strong swirling flow is generated in each large cavity portion 8. Thereby, the air around the large cavity portion 8 is widely taken in, and the combustion is rapidly diffused. In addition, some jets are distributed
Although the vehicle goes straight after going over 0, it is also smoothly guided to each large cavity portion 8 by the opposing wall portion 9.

Here, since the jet flowing straight along the jet center line L as described above is restricted by the dispersion table 10, the jet collides with the cylinder bore 4 over the opposing wall 9 to extinguish the flame. Is less. That is, it is possible to suppress the flame extinction due to the collision with the cylinder bore 4 while enhancing the swirling flow in the large cavity portion 8.

A part of the jet colliding with the dispersion table 10 and diffused into the passage 11 joins the swirling flow of the large cavity 8 through the passage 11 from a substantially radial direction as shown by an arrow b. Therefore, the swirling flow in the large cavity 8 is disturbed, and the gas flow is activated to further promote the mixing of the air and the fuel.

Therefore, the air utilization rate in the main combustion chamber 5 can be further increased, and the emission of unburned fuel at low load 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, a lateral cavity portion 13 extending left and right along the periphery of the piston 3 from below the injection port 7 is added to the injection port 7 side of the top surface of the piston 3. The side cavities 13 also serve as the passages 11 of the first embodiment described above, have the same depth as the large cavities 8, and have the large cavities 8 on both the left and right sides of the pair of dispersion tables 10. It is continuous with one. The outer shell 13a of the side cavity portion 13 on the rear side of the injection port 7 has an arc shape along the periphery of the piston 3. Outer shells 1 on both sides
3b is smoothly curved and extends obliquely toward the center of the piston 3, and guides the jet flowing out of the side cavity portion 13 in a substantially tangential direction of the swirling flow generated in the large cavity portion 8. ing. The configurations of the large cavity 8 and the guide groove 12 are basically the same as those of the first embodiment.

In the second embodiment, the combustion gas colliding with the dispersion table 10 diffuses widely into the side cavity 13 as indicated by an arrow a in FIG. Can be used more effectively.
Then, the jet flow directed to the side cavity portion 13 joins the swirling flow indicated by the arrow b in the large cavity portion 8 reinforced by the guide groove 12 from a substantially tangential direction as indicated by the arrow c. Therefore, although the turbulence in the large cavity 8 is relatively small, the swirling flow in the large cavity 8 can be further strengthened.

Next, FIGS. 5 and 6 show a third embodiment of the present invention. In this embodiment, spiral concavities 14 are respectively formed on the bottom surface of the large cavity portion 8, and each concavity 14 has the deepest center portion and a swirl flow generated in each large cavity portion 8. Is formed so as to gradually become deeper along the forward direction of the first direction. That is, it has a spiral side wall surface 14a so that the turning radius gradually decreases.

Therefore, in the configuration of this embodiment, even if the speed of the jet jetting out from the jet port 7 gradually decreases with the progress of the combustion, when the jet jet approaches the central portion in the large cavity portion 8, the side wall surface will not move. Since the turning radius is restricted to a small value by 14a, a turning flow with a sufficient flow velocity can be secured for a long period of time. In addition, since the air existing in the recess 14 is pushed out and diffused by the swirling flow, the mixing of the fuel and the air is further promoted.

[0025]

As is apparent from the above description, according to the combustion chamber of the swirl chamber type diesel engine according to the present invention, a part of the jet collides with the dispersion table and diffuses widely, and at the same time, the center of the dispersion table is A part of the jet flow is guided from the circumferential direction to the large cavity portion along the guide groove passing therethrough while maintaining a strong flow, so that a strong swirling flow can be generated in the large cavity portion. That is, it is possible to achieve both the initial wide diffusion of the combustion gas and the strong swirling flow in the large cavity portion, and it is possible to further increase the air utilization rate on the main combustion chamber side. Therefore, it is possible to suppress the discharge of the unburned fuel at a low load and to reduce the smoke at a high load.

[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;

FIG. 5 is a plan view of a piston top surface showing a third embodiment of the combustion chamber according to the present invention.

FIG. 6 is a cross-sectional view of the top of the piston taken along line CC of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 3 ... Piston 5 ... Main combustion chamber 6 ... Swirl chamber 7 ... Injection port 8 ... Large cavity part 9 ... Opposing wall part 10 ... Dispersion table 11 ... Path part 12 ... Guide groove 13 ... Side cavity part (path part) 14 ... Concave part

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-43619 (JP, A) JP-A-1-200012 (JP, A) JP-A-1-118122 (JP, U) JP-A-63 104634 (JP, U) Japanese Utility Model 63-100633 (JP, U) Japanese Utility Model 63-79435 (JP, U) Japanese Utility Model 58-8715 (JP, U) (58) Fields surveyed (Int. 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 continuous with each other at the center, and a groove narrower than the opening width of the nozzle and deeper than the large cavity, and extending from the lower part of the nozzle, A guide groove extending along the jet center line, the tip end side being formed gradually shallower, and a forked bifurcated tip portion connected to each large cavity portion from the circumferential direction, and a nozzle of the large cavity portion Forming a part of the outer shell on the side, and a pair of dispersion tables that are raised so as to sandwich the guide groove from both sides, and are recessed at substantially the same depth as the large cavity portion, and Pass through the side of the dispersion table A swirl chamber comprising: a passage portion continuous with the cavity portion; and a connecting portion between the pair of large cavities, and an opposing wall portion formed as a part of the outer shell and extending toward the injection port. Combustion chamber of a diesel engine.