JP2797794B2 - 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
No. 00012, etc., on the top surface of the piston, a pair of large cavities are recessed across the center line of the jet from the nozzle, and the dispersion table is raised in an island shape on the center line and near the nozzle, and A combustion chamber structure is proposed in which side cavities communicating with the large cavities are formed on both sides on the front side 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] The side cavity portion is provided for positively performing the diffusion combustion in the initial stage, and the combustion gas which has collided with the dispersing stage at the beginning and is dispersed is subjected to the side cavity portion. As a result, the air in the side cavity portion is immediately taken in, and the initial diffusion combustion on the main combustion chamber side is promoted.

[0006]

However, in the configuration in which the dispersion table is provided on the top surface of the piston as described above, the dispersion table locally protrudes in the main combustion chamber, and the jet from the vortex flow chamber is strongly intensified. Therefore, the heat load tends to be high partially, which is not preferable in terms of durability and the like.

Therefore, an object of the present invention is to provide a combustion chamber structure which can similarly increase the air utilization rate without using a dispersion table.

[0008]

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 swirl chamber is directed toward the center of the main combustion chamber, and a recess provided on a top surface of the piston. And a pair of large cavities, each of which extends substantially circularly to the left and right across the center line of the jet, and is recessed at a position near the injection port on the top surface of the piston. While expanding, the side cavity part communicating with the large cavity part and a part of an outer shell defining the side cavity part are formed, and the jet flow from the side cavity part is substantially equivalent to a swirling flow in the large cavity part. A vortex chamber type diesel engine comprising: a tangential guide wall; and an opposing wall formed at a connection between the pair of large cavities as a part of the outer shell and extending toward the injection port. In the combustion chamber In the side cavity portion around the injection port extension position at the top dead center position, an outer shell on the rear side of the injection port forms a substantially elliptical concave portion substantially similar to the outer shell of the side cavity portion, and As the outer shell on the large cavity side of the concave portion, a diffusion wall portion is formed in which a portion near the center line of the jet from the jet port is relatively deeper than left and right portions.

Further, in the invention of claim 2, the bottom surface of the concave portion is an inclined surface that becomes deeper from the rear side of the injection port toward the large cavity portion.

[0010] In the invention of claim 3, the bottom surface of the concave portion is formed so as to be relatively deep on the center line of the jet from the jet port and relatively shallow toward the left and right ends.

Further, in the invention according to claim 4, a dome-shaped projection is provided at the injection port extension position of the concave portion at the piston top dead center position.

[0012]

The flame-like combustion gas ejected from the swirl chamber through the injection port first diffuses into the recess near the top dead center of the piston.
In other words, the air in the concave portion is immediately taken in and diffuses and burns, and spreads to the surroundings. Here, the jet has a strong velocity component that travels straight along the nozzle, but because it collides with the diffusion wall that is the outer shell of the concave portion, some jets go to the side cavity and take in air in this part. go.

Further, a part of the jet flow goes straight over the diffusion wall portion of the concave portion and is divided by the opposing wall portion to generate a swirling flow in the large cavity portion, so that air near the large cavity portion is effectively used. Then, the jet flow directed to the side cavity portion merges into the large cavity portion from the substantially tangential direction of the swirling flow along the guide wall portion.

[0014] Since the diffusion wall portion is deeper near the center line of the jet from the nozzle, the combustion gas diffused in the recess extends toward the center line and reduces the straight component of the jet. Does not overly weaken.

[0015] If the bottom surface of the concave portion is an inclined surface, the volume of the concave portion is reduced as compared with the required height of the diffusion wall portion, which is advantageous in terms of compression ratio and the like.

According to the third aspect of the present invention, the swirling flow in the large cavity portion can be relatively strong without excessively weakening the straight component of the jet.

Further, according to the structure of the fourth aspect, the initial jet flow spouted from the injection port collides with the dome-shaped projection and is diffused, so that the initial diffusion combustion is improved.

[0018]

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 swirl chamber 6 is located along the side of the cylinder head 2, and an injection port 7 extending from the swirl 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, which serves as a connection between the two,
, And form an opposing wall 9 that partitions the two large cavities 8.

At a position near the injection port 7 on the top surface of the piston 3, a side cavity portion 10 is provided which is widened right and left along the peripheral edge of the piston 3 from below the injection port 7. The side cavity portion 10 has a constant depth in each portion, specifically, the same depth as the large cavity portion 8, and the side cavity portion 10 and the large cavity portion 8 are located in front of the injection port 7. The parts communicate with each other integrally. The outer shell 11a of the side cavity portion 10 on the rear side of the injection port 7 is
It has an arc shape along the periphery. The outer shells on the left and right sides are smoothly curved toward the center of the piston 3, and guide the jet flowing out of the side cavity 10 in a substantially tangential direction of the swirling flow generated in the large cavity 8. The portion 11b is formed. The wall surface of the outer shell forming the large cavity portion 8 and the side cavity portion 10 is perpendicular to the top surface of the piston 3.

Inside the side cavity portion 10, a substantially oval concave portion 12 is formed relatively shallowly.
The recess 12 is formed around an extended position (shown by an imaginary line in FIG. 1) of the nozzle 7 at the piston top dead center position, and the outer shell 12 a on the rear side of the nozzle 7 is
The outer shells 12a at the left and right ends are also smoothly curved toward the center of the piston 3 inside the guide wall 11b. The outer shell 12c on the side of the large cavity portion 8 extends toward the large cavity portion 8 only at the center thereof, that is, near the center line L, and the outer shell 12c on the side of the large cavity portion 8 extends.
c forms a diffusion wall portion 12 d perpendicular to the top surface of the piston 3. As shown in FIG. 2, the bottom surface of the concave portion 12 is formed as a gentle inclined surface that gradually becomes deeper from the rear side of the injection port 7 toward the large cavity portion 8. In addition, since the bottom surface of the concave portion 12 is inclined as described above, as the diffusion wall portion 12d, as shown in FIG. 3, the central portion extending to the side of the largest cavity portion 8 is deepest, and The left and right ends are shallower than this.

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

The fuel injected into the swirl chamber 6 before the compression top dead center is ignited in the swirl chamber 6, and becomes a flame containing unburned fuel near the compression top dead center and is ejected from the injection port 7. The jet of the combustion gas first collides with the bottom surface of the concave portion 12 where the injection port 7 faces,
Spread around. At this time, the air existing in the concave portion 12 is immediately taken into the flame, so that the initial diffusion combustion becomes good. Further, due to the collision described above, the jet flow spreads to the left and right of the side cavity portion 10 and takes in the air around it. The jet flowing toward the side is guided to the large cavity portion 8 along the outer shells 12b at the left and right ends of the concave portion 12 and the guide wall portion 11b of the side cavity portion 10, and is indicated by an arrow a in FIG. As shown, the fluid smoothly merges with the swirling flow in the large cavity portion 8 from the tangential direction. Since the bottom surface of the concave portion 12 is an inclined surface and the injection port 7 itself is also inclined toward the center of the piston 3, the injection port 7
The flame that extinguishes toward the rear is very small.

On the other hand, most of the jet flowing out of the jet port 6 tends to flow along the center line L, but this flow collides with the diffusion wall portion 12d forming the outer shell of the concave portion 12 and is partially dammed. Therefore, a part of the jet is widely diffused to the side. In other words, the air flowing in the vicinity of the side cavity 10 can be effectively used without passing through the vicinity of the side cavity 10 due to the strong straight traveling velocity component of the jet.

A part of the jet colliding with the diffusion wall 12d or the jet traversing straight without colliding with the diffusion wall 12d flows into the large cavity 8 as shown by an arrow b or an arrow c in FIG. A swirling flow is generated in each large cavity portion 8. Thereby, combustion is diffused while taking in the air in the main combustion chamber 5. At this time, since the jet flowing straight along the center line L is smoothly guided to each large cavity portion 8 by the opposing wall portion 9, a swirling flow is well formed and the jet flow passes over the large cavity portion 8. The flame colliding with the wall surface of the cylinder bore 4 can be suppressed.

Further, in the concave portion 12, the vicinity of the center line L extends toward the large cavity portion 8, and this portion is relatively deep, so that the flame diffuses toward the direction where a large amount of air is present at the beginning. Try to go. Therefore, at the stage of moving to the large cavity portion 8, the component traveling along the center line L increases, and a strong swirling flow can be generated in the large cavity portion 8. That is, the straight traveling speed component is not excessively weakened by the diffusion wall portion 12d,
The generation of the swirling flow in the large cavity 8 is not hindered.

In this manner, good combustion with a high air utilization rate can be ensured over a wide range of the main combustion chamber 5, and smoke and HC can be reduced. And in the above configuration,
Since there are no local protrusions exposed to high temperatures in the main combustion chamber 5, it is advantageous in terms of heat load as compared with those having a dispersion table. On the other hand, if the recess 12 is provided on the main combustion chamber 5 side as described above, it is disadvantageous in securing the compression ratio and the volume of the vortex chamber 6, but as in the above embodiment, the bottom surface of the recess 12 is inclined. By doing so, the volume of the entire concave portion 12 can be made very small while sufficiently securing the height of the diffusion wall portion 12d. It is to be noted that inclining the bottom surface is also advantageous in suppressing the flame from flowing toward the rear of the nozzle 7 as described above.

Next, FIGS. 4 and 5 show a second embodiment of the present invention.
An example is shown. In this embodiment, the planar outer shell shape of the concave portion 12 is an elliptical shape that is substantially symmetrical between the rear side and the front side of the nozzle 7. Further, the bottom surface forms a gentle slope gradually deepening from the rear side of the injection port 7 toward the large cavity portion 8 as in the above-described embodiment. In particular, as shown in the cross-sectional view of FIG. The portion along the jet center line L is relatively deep, and has a gentle V-shaped cross section that gradually becomes shallower toward the left and right ends. That is, also in this embodiment, as the diffusion wall portion 12d, the vicinity of the center line L is deepest.

Therefore, in this embodiment, while the jet flow is widely diffused right and left by the concave portion 12 and the diffusion wall portion 12d, the effect of guiding the flame in the straight traveling direction to generate a good swirling flow in the large cavity portion 8 is compared. Become stronger. still,
In the recess 12 having a flat outer shell shape as in the first embodiment described above, the bottom surface may have a gentle V-shaped cross section as shown in FIG.

Next, FIGS. 6 and 7 show a third embodiment of the present invention.
An example is shown. In this embodiment, a circular dome-shaped projection 15 is formed at the center of the bottom surface of the recess 12, more specifically, at the extended position of the injection port 7 at the top dead center position of the piston 3. The jet that erupted from
The projection 15 collides with the projection 15. Therefore, the combustion gas diffuses widely in the concave portion 12 along the surface shape of the projection 15, and the air utilization rate in the concave portion 12 is improved in the early stage of the combustion on the main combustion chamber 5 side, and smoke and HC are reduced.
Is further reduced.

[0033]

As is clear from the above description, in the combustion chamber of the swirl chamber type diesel engine according to the present invention, the recesses provided in the side cavities extend to the left and right of the side cavities similarly to the dispersion table. The jet can be diffused, and together with the swirling flow in the large cavity, the air utilization can be increased over the entire area of the main combustion chamber. And
Since a local protrusion is not used unlike a dispersion table, it is advantageous in terms of heat load and durability.

Also, when the jet begins to erupt from the nozzle,
Since the air in the concave portion is immediately taken in and burned, the start of combustion on the main combustion chamber side is prompt, and smoke and HC are further reduced.

If the bottom surface of the concave portion is formed as an inclined surface on the large cavity side, the volume of the concave portion can be reduced while the function of the diffusion wall portion is maintained.

If the bottom surface of the concave portion is made deeper on the center line of the jet, the jet quickly diffuses toward the large cavity portion, and the swirling flow on the large cavity portion side can be relatively strengthened.

Further, according to the configuration in which the projection which collides with the jet flow is provided on the bottom surface of the concave portion, the diffusion of the initial jet flow is further promoted,
The air utilization rate in the recess is further improved.

[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 sectional view taken along the line AA of FIG. 1 showing the combustion chamber of the first embodiment.
Sectional view along the line.

FIG. 3 is a sectional view taken along the line BB of FIG. 1;

FIG. 4 is a plan view of a piston top surface according to a second embodiment of the present invention.

FIG. 5 is a sectional view taken along the line CC of FIG. 4;

FIG. 6 is a plan view of a piston top surface showing a third embodiment of the present invention.

FIG. 7 is a sectional view similar to FIG. 1, showing a combustion chamber of a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 3 ... Piston 5 ... Main combustion chamber 6 ... Swirl chamber 7 ... Injection port 8 ... Large cavity part 9 ... Opposite wall part 10 ... Side cavity part 11b ... Guide wall part 12 ... Concave part 12d ... Diffusion wall part 15 ... Projection

Claims (4)

(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, each of which expands in a substantially circular shape to the left and right, and a recessed portion at the top of the piston near the injection port, spreads right and left along the periphery of the piston from near the bottom of the injection port, and A communicating side cavity portion, and a guide wall portion which forms a part of an outer shell defining the side cavity portion and guides a jet flow from the side cavity portion in a substantially tangential direction of a swirling flow in the large cavity portion. In a combustion chamber of a swirl chamber type diesel engine, a piston is formed in a connection portion of a pair of large cavities, and an opposing wall portion formed as a part of the outer shell and extending toward the injection port. Spout at point location An outer shell on the rear side of the injection port forms a substantially elliptical concave portion substantially similar to the outer shell of the side cavity portion in the side cavity portion around the extension position, and the concave portion has a large cavity portion side. A combustion chamber of a vortex chamber type diesel engine, characterized in that a diffusion wall portion in which a portion near a center line of a jet from an injection port is relatively deeper than left and right portions is formed as an outer shell of the combustion chamber. 2. The combustion chamber of a vortex chamber type diesel engine according to claim 1, wherein the bottom surface of the concave portion is an inclined surface that becomes deeper from the rear side of the injection port toward the large cavity portion. 3. The bottom surface of the concave portion is formed so as to be relatively deep on the center line of the jet from the nozzle and relatively shallow toward the left and right ends. The combustion chamber of the vortex chamber type diesel engine described. 4. The combustion chamber of a vortex chamber type diesel engine according to claim 1, wherein a dome-shaped projection is provided at an injection port extension position of the recess at a piston top dead center position.