JPH089968B2 - Combustion chamber structure of direct injection diesel engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion chamber structure of a direct injection diesel engine, and more particularly, to a combustion chamber formed eccentrically from the center of a cylinder bore. The present invention relates to a combustion chamber structure of a direct injection diesel engine for improving the air flow of the diesel engine.

[Prior Art] In a direct injection diesel engine, a lip is formed in the upper part of the combustion chamber defined in the piston head so as to project inward in the radial direction from the combustion chamber, and the air flow of squish, swirl, etc. is made efficient. It is often introduced into the combustion chamber to mix fuel vaporization,
It is known that a combustion chamber structure referred to as a shelf type or a reentrant type is adopted for improving the air utilization rate (Japanese Patent Laid-Open No. 507071/1975). In general, the combustion chamber is defined and formed in the piston head so as to be aligned with the center of the cylinder bore, and the lip is formed so as to protrude equally along the circumferential direction of the combustion chamber so as to equally cover the peripheral portion of the combustion chamber. The uniform squish and swirl are obtained throughout the combustion chamber. That is,
Generally, the center of the combustion chamber and the center of the opening of the combustion chamber defined by the lip are both formed to coincide with the center of the cylinder bore.

[Problems to be Solved by the Invention] In a small engine or the like having a small cylinder bore diameter, the fuel injection nozzle cannot be located at the center of the cylinder bore because of the installation of intake and exhaust valves. Therefore, the fuel injection nozzle is installed eccentric from the center of the cylinder bore. Further, the combustion chamber needs to be formed so that the distance from the fuel injection nozzle to the inner peripheral wall thereof is equal, that is, the center of the combustion chamber coincides with the installation position of the fuel injection nozzle. As a result, in an engine in which the fuel injection nozzle is eccentric from the center of the cylinder bore, the center c of the combustion chamber a must be eccentric from the center b of the cylinder bore as shown in FIGS. 3 and 4. I have to. Therefore, in such an engine, the swirl d and the squish e generated in the combustion chamber a become non-uniform, and there is a problem that the mixture vaporization of the fuel is hindered and the smoke is deteriorated and the engine output is reduced.

Explaining the swirl d, the swirl d is swirling in the cylinder, and due to its centrifugal force, is swirling at high speed with high air density on the cylinder inner peripheral wall side that is the centrifugal side radially outward from the cylinder bore center b. It turns at low speed with a lean air density on the side.
As a result, the swirl d introduced into the combustion chamber a has strong momentum on the centrifugal side of the cylinder bore (indicated by d ₁ in the figure) and weak on the center b side (indicated by d ₂ in the figure). Therefore, the swirl d in the combustion chamber a is in a non-uniform state.

In addition, squish e will be explained.
Is affected by the swirl d described above, and the squish e does not grow sufficiently on the centrifugal side of the cylinder bore due to the presence of the strong swirl d ₁ , while the squish e grows sufficiently on the center b side because the swirl d ₂ is weak. Have become dominant. As a result, the squish e introduced into the combustion chamber a
Is strong on the side of the center b of the cylinder bore (indicated by e ₁ in the figure) and weak on the centrifugal side (indicated by e ₂ in the figure), and the squish e in the combustion chamber a is also non-existent. It is in a uniform state.

Thus, in the combustion chamber a, the center b of the cylinder bore is
Stronger squish e ₁ , weaker swirl d ₂ airflow is introduced, stronger swirl d ₁ , weaker squish e ₂ than centrifugal side
Since the above air flow is introduced, the inside of the combustion chamber a is excessively non-uniform due to these air flows, which impedes the fuel vaporization.

[Means for Solving the Problems] The present invention is directed to a direct injection diesel engine in which a combustion chamber is formed by offsetting from the center of a cylinder bore, and a lip is provided at the opening of the combustion chamber over the entire circumference thereof. In the above combustion chamber structure, the protrusion length of the lip is changed to form a polygonal opening of the combustion chamber as viewed from above, and the protrusion length of this lip is made longer on the offset side and shorter on the opposite side. The corners of the opening on the offset side are rounded with a small radius, and the corners on the side opposite to the offset side are rounded with a radius larger than that of the offset side.

[Operation] The introduction of squish into the combustion chamber is affected not only by the position where the combustion chamber is formed with respect to the center of the cylinder bore, but also by the amount of lip overhang. Then weakened. Therefore, the amount of protrusion of the lip on the offset side is made larger than the lip on the side opposite to the offset side, which is stronger than the squish, to make the squish uniform in the combustion chamber. Regarding the introduction of the swirl into the combustion chamber, the swirl is attenuated as the shape of the opening through which the swirl flows into the combustion chamber becomes steeper or the shape changes significantly. Therefore, the shape of the opening on the offset side, more specifically, the shape of the corner of the swirl, which is weaker on the offset side than on the opposite side, is made steep to make the swirl uniform in the combustion chamber.

The air flow generated in the combustion chamber is improved by making the squish and swirl uniform.

[Embodiment] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIGS. 1 and 2, in the piston head 1, a polygonal combustion chamber 2 such as a quadrangle is formed by being depressed at a position eccentric from the cylinder bore center C ₁ . And, in particular, the opening 3 of the combustion chamber 2 is formed in a polygonal shape with a smaller diameter than the bottom portion 4 which does not protrude from the bottom portion 4 of the combustion chamber 2, and the center C ₂ thereof is further burned. It is formed eccentrically to the cylinder bore center C ₁ side with respect to the center C _{3 of the} chamber 2.

In the illustrated example, the opening 3 is formed in a shape substantially similar to the shape of the bottom surface portion 4. Since only the opening 3 is eccentric to the cylinder bore center C ₁ side with respect to the combustion chamber 2 and is formed with a diameter that does not protrude from the bottom surface portion 4, the upper portion of the combustion chamber 2 along the circumferential direction thereof. A lip 5 is formed radially inward of the combustion chamber 2 so as to project like an eaves. And this lip 5
Is divided into the side portion 6 of the bottom surface portion 4 of the combustion chamber 2 on the centrifugal side and the side portion 7 of the opening portion 3 on the centrifugal side from the cylinder bore center C ₁ and greatly expands inward of the combustion chamber 2 while sandwiching the opening portion 3. Overhanging portion 5a and bottom portion 4 of combustion chamber 2 on the cylinder bore center C ₁ side
And a side portion 9 of the opening 3 on the side of the center C ₁ which is divided into a side portion 8 and a side portion 5b which is extended to the inside of the combustion chamber 2 while expanding the opening portion 3 and these portions 5a, 5b. It is configured to be formed along the circumferential direction of the combustion chamber 2 via a portion 5c that is divided into other side portions that are connected while gradually increasing and gradually decreasing the amount of protrusion of the lip 5 between the spaces.

In this way, the amount of protrusion of the lip 5 is gradually increased from the cylinder bore center C ₁ side toward the centrifugal side along the circumferential direction of the combustion chamber 2, and the amount of protrusion of the lip portion 5a on the centrifugal side is the center C ₁
By forming the squish Sq larger than the side lip portion 5b, the strength of the squish Sq can be adjusted, and even if the combustion chamber is eccentric from the cylinder bore center C ₁ , the squish Sq to be generated inside the squish Sq is entirely in the combustion chamber 2. Can be made uniform over the entire length.

On the other hand, in the opening 3 formed in a polygonal shape and having a plurality of corners 10 and 11, among these corners 10 and 11, the corner 10 connected to the side 9 on the cylinder bore center C ₁ side has a large radius R _1. And the corner portion 11 connected to the side portion 7 on the centrifugal side is rounded with a smaller radius R ₂ (R ₁ > R ₂ ). This is the corner 10,11
By changing the radii R ₁ and R ₂ of the cylinder bore center C ₁ side and the centrifugal side to form the shape of the opening 3 gently on the cylinder bore center C ₁ side and sharply on the centrifugal side, the swirl Sw The strength can be adjusted, and even in the combustion chamber 2 that is eccentric from the cylinder bore center C ₁ , the swirl Sw to be generated inside the combustion chamber 2 can be made uniform throughout the entire combustion chamber 2.

 Next, the operation of the embodiment will be described.

During the compression stroke of the direct injection diesel engine, airflows such as squish Sq and swirl Sw are generated in the cylinder and introduced into the combustion chamber 2. In these air streams,
The strength of the squish Sq is determined by the amount of protrusion of the lip 5, and is strong at the portion 5a where the amount of lip protrusion is large and weak at the portion 5b where the amount of lip protrusion is small.
Therefore, these lip portions 5a, 5b, 5c supplement and strengthen the squish Sq on the centrifugal side of the cylinder bore, and suppress and weaken the squish Sq on the center C ₁ side, so that a uniform squish Sq in the combustion chamber 2 is obtained.
Can be generated.

Further, the swirl Sw has its strength determined by the shape of the opening 3 through which it is introduced into the combustion chamber 2, the opening shape is strongly maintained at the gentle corner portion 10, and the opening shape is sharp at the sharp corner portion 11. Attenuated. Therefore, these corners 10 and 11 strongly maintain the swirl Sw on the side of the center C _{1 of} the cylinder bore, attenuate the swirl Sw on the centrifugal side, and make the swirl even in the combustion chamber 2.
Sw can be generated.

The squish Sq and swirl Sw that are made uniform by the shapes of the lip 5 and the opening 3 can generate a uniform and appropriate turbulent flow throughout the combustion chamber 2.

As described above, since the inside of the combustion chamber 2 can be made to be uniformly turbulent, it is possible to promote the mixed vaporization of the injected fuel, improve NOx, smoke and the like, and improve the engine output.

[Effects of the Invention] In summary, according to the present invention, the following excellent effects are exhibited.

The strength of squish and swirl can be made uniform, and even swirl and squish can be generated throughout the combustion chamber that is eccentric from the center of the cylinder bore to ensure uniform turbulence and promote fuel vaporization. it can.

[Brief description of drawings]

FIG. 1 is a plan view showing a preferred embodiment of the present invention, FIG. 2 is a sectional view taken along the line II-II in FIG. 1, FIG. 3 is a plan view showing a conventional example, and FIG. FIG. 4 is a sectional view taken along the line IV-IV in the figure. In the figure, 2 is a combustion chamber, 3 is an opening, 5 is a lip, 10 and 11 are corners, and C ₁ is the center of the cylinder bore.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-29018 (JP, A) JP-A-59-203816 (JP, A) Actually open 59-68128 (JP, U) Actual-open Sho-60- 87338 (JP, U) Actually opened 57-95426 (JP, U) Actually opened 60-1921 (JP, U) Special public Sho 56-7494 (JP, B2) Actual public 59-33863 (JP, Y2) Actual public Sho 60-19957 (JP, Y2)

Claims (1)

[Claims] 1. A combustion chamber structure of a direct injection diesel engine, wherein a combustion chamber is formed offset from the center of a cylinder bore, and a lip is provided at the opening of the combustion chamber over the entire circumference thereof. While changing the protruding length to form the opening of the combustion chamber seen from above in a polygonal shape,
The protruding length of the lip is made longer on the offset side and shorter on the opposite side, and the corners on the offset side of the opening are rounded with a small radius, and the corners on the side opposite to the offset side are more than the corners on the offset side. Combustion chamber structure of direct injection diesel engine characterized by rounding with a large radius.