JPH0648108Y2 - Combustion chamber of swirl chamber type diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to improvement of a combustion chamber shape of a swirl chamber type diesel engine.

(Prior Art) Fig. 3 shows the shape of the main combustion chamber of a swirl chamber type diesel engine.
The ones shown in A and B are known. Explaining this, a swirl chamber 5 provided in the cylinder head 4 so as to be located offset from the center of the cylinder communicates with the main combustion chamber 9 through an injection port 6, and the top surface 8 of the piston 3 has the above-mentioned structure. A groove-shaped trench portion 26 extending in a radial direction from a region substantially directly below the main combustion chamber side opening of the injection port 6, and the trench portion 26.
A substantially circular cavity portion 10 is formed which spreads from the region near the center of the piston to both sides, and these constitute a so-called cloverleaf type cavity.

In this swirl chamber type combustion chamber structure, the air flowing from the main combustion chamber 9 through the nozzle 6 into the swirl chamber 5 in the compression stroke forms a swirl. Combustion is started by injecting and supplying fuel to this swirl flow through an injection nozzle (not shown), and with the start of combustion in this swirl chamber 5, the expanded gas and part of the injected fuel are injected through the injection port 6. It jets out to the main combustion chamber 9. The fuel in the jetted gas is guided toward the center of the main combustion chamber 9 along the trench portion 26 of the piston 3, and further diffuses as a swirling flow into the cavity portions 10 on both sides as indicated by the arrow a. To do. As a result, the fuel is mixed with the air in the main combustion chamber in the range indicated by the broken line in the figure and burns. (For known examples of this type of combustion chamber structure, see, for example, Japanese Utility Model Laid-Open No. 57-174725, etc.) (Problems to be solved by the invention) However, in such a conventional swirl chamber combustion chamber, Then, since the trench portion 26 is along the direction of the jet flow from the swirl chamber 5, the force of the jet flow proceeding from the nozzle 6 along the trench portion 26 in the radial direction is relatively large, and the cavity portion 10 Initially, the force of the jet flow diffusing to the side of the trench portion 26 becomes relatively weak. Therefore, especially near the base end of the trench portion 26, which is upstream of the jet flow, and on both sides thereof, the fuel and air are not sufficiently mixed, and the air utilization ratio tends to be small. This causes an increase in the concentration of unburned fuel components in the exhaust during a low load operation and an increase in the smoke concentration during a high load operation.

The present invention aims to solve these conventional problems.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, a piston top is provided in a combustion chamber of a swirl chamber type diesel engine in which an injection port from the swirl chamber is opened near the edge of the main combustion chamber. On the surface, the left and right large cavity portions that spread out in a substantially circular shape from the region near the center of the piston, and the left and right side cavity portions that branch from the trench portion that is below the injection port and communicate with each of the large cavity portions are formed. The depth of the lateral cavity is formed to be larger than that of the large cavity and smaller than that of the trench, and the outer wall defining the lateral cavity is tangential to the outer wall of the large cavity adjacent to the lateral cavity. The guide part that faces the outer side of the large cavity part and is positioned between the left and right side cavity parts. Then, the dispersion base having a shape in which a part of its outer shape facing the side cavity portion substantially corresponds to the guide portion was raised.

(Operation) In the above-mentioned configuration, the jet flow is diffused through the lateral cavity portion even in a region where the jet flow from the swirl chamber is hard to flow, that is, both sides immediately below the jet port. Further, the flow of combustion gas in the lateral cavity is guided in a direction tangential to the flow in the large cavity by the guide part and the dispersion table formed between the left and right lateral cavity parts correspondingly. Therefore, the tangential flow enhances the swirling flow in the large cavity. As a result of these, the air utilization rate is increased over the entire area of the main combustion chamber.

In this way, the jet of the combustion gas containing the fuel is sufficiently diffused over a wide range of the main combustion chamber, so that the air in the main combustion chamber is effectively used and good combustion properties are obtained.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings.
The parts corresponding to those in FIGS. 3A and 3B are designated by the same reference numerals.

In FIG. 1A or FIG. 1B, 11 is the piston top surface 8
It is a groove-shaped trench portion that extends from immediately below the injection port 6 along the center line 1 of the jet flow toward the piston center. Trench
The passage width of 11 is formed smaller than the opening width of the injection port 6.

The reference numeral 12 designates a large cavity portion which spreads in a substantially circular shape on both sides of the trench portion 11 from a region near the center of the piston top surface 8 and which has a shape in which arcs are symmetrically arranged across the center line 1 of the jet flow. Defined by outer shell 17. The outer shell 17 is formed with a facing wall portion 17a which projects in a substantially V shape on the jet center line l.

Reference numeral 14 denotes a lateral cavity portion that extends from the trench portion 11 below the injection port 6 to both sides and communicates with the large cavity portion 12,
It is defined by an island-shaped raised dispersion stand 15 and an outer shell 18 as a guide. The outer shell 18 as the guide portion extends in a circular shape along the outline of the piston 3 from the trench portion 11 to the middle thereof, and the curvature is gradually reduced from the middle thereof.

The dispersion table 15 is arranged between the side cavity portions 14 and the large cavity portion 12 so as to sandwich the trench portion 11.

The depth of the lateral cavity portion 14 with respect to the piston top surface 8 is
It is formed smaller than the trench portion 11 and larger than the large cavity portion 12.

A step 14a is formed between the bottom surface 14e of the side cavity portion 14 and the bottom surface 12e of the large cavity portion 12 in an arc shape along the outline of the large cavity portion 12.

The bottom surface 11e of the trench portion 11 is formed so as to be inclined toward the bottom surface 12e of the large cavity portion 12.

Based on the above configuration, the jet containing unburned fuel ejected from the swirl chamber 5 to the main combustion chamber 9 through the injection port 6 in the expansion stroke hits the bottom surface 11e of the trench portion immediately below the injection port 6 having a large depth, and most of it goes straight. However, a part of them diffuses over the opposed wall portion 17a and diffuses on the piston top surface 8, and the rest diffuses into the left and right large cavity portions 12 and is guided by the outer shell 17 as shown by an arrow b in the figure. A swirl flow is generated.

Since the lateral cavity portion 14 is formed on the lateral side of the trench portion 11 with an appropriate depth shallower than the trench portion 11,
A part of the jet gas containing the unburned components ejected to the main combustion chamber 9 through the jet port 6 is divided into the lateral cavity portion 12 from the trench portion 11 as shown by the arrow c, and the dispersion table is generated. The swirl flow generated in the large cavity portion 12 is guided by the outer shell 15 and the outer shell 18 and joins in a substantially tangential direction.

By making the depth of the lateral cavity portion 14 larger than that of the large cavity portion 12 and forming a step 14a at the boundary between the lateral cavity portion 14 and the large cavity portion 12 at a predetermined height, the lateral cavity portion 14 is formed. The flow rate at which the split flow (arrow c) merges with the swirl flow (arrow b) generated in the large cavity portion 12 can be appropriately set, and the turbulence imparted to this swirl flow can be reduced.

As a result, as shown by the broken line in the figure, the diffusion region of the jet flow is extremely wide, and therefore the air in the main combustion chamber 9 can be fully utilized for efficient combustion.

Another embodiment shown in FIGS. 2A and 2B is a piston top surface 8
In addition, an island-shaped protruding dispersion stand 25 is formed on the jet flow center line l, and the outer shell 25a facing the injection port 6 has a substantially V shape and is projected.

Reference numeral 21 denotes a curved groove-shaped trench portion that extends around both sides of the dispersion table 25 and communicates with the large cavity portions 12 on the left and right.

The lateral cavity portion 24 extends from the trench portion 21 to both sides and communicates with the large cavity portion 12, and has a depth smaller than that of the trench portion 21 and larger than that of the large cavity portion 12.

A step 24a is formed between the bottom surface 24e of the side cavity portion 24 and the bottom surface 12e of the large cavity portion 12 in an arc shape along the outline of the large cavity portion 12.

The bottom surface 21e of the trench portion 21 is inclined toward the bottom surface 12e of the large cavity portion 12.

By disposing the dispersion table 25 on the jet flow center line 1 based on the above configuration, the jet flow including unburned fuel ejected from the swirl chamber 5 to the main combustion chamber 9 through the injection port 6 in the expansion stroke is
Colliding with the dispersion table 25 located immediately downstream of the same, shunting to the left and right trench portions 21 as shown by the arrow d, and being guided by each trench portion 21 and colliding with the substantially V-shaped facing wall portion 17a. Then, a swirl flow is generated in the left and right large cavity portions 12.

Also in this case, since the lateral cavity portion 24 is formed on the lateral side of the trench portion 21 with an appropriate depth shallower than that of the trench portion 21, the unburned components ejected to the main combustion chamber 9 through the injection port 6 are removed. As shown by arrow e, a part of the jet gas containing the flow splits from the trench portion 21 to the lateral cavity portion 24, and a step 25 is formed at the boundary between the lateral cavity portion 24 and the large cavity portion 12 at a predetermined height. Since the flow is divided into the lateral cavity 24 (arrow e) and the swirl flow (arrow d) generated in the large cavity 12, the flow rate can be set appropriately. Reduces the turbulence imparted to the swirling flow.

As a result, as shown by the broken line in the figure, the diffusion region of the jet flow is extremely wide, and therefore the air in the main combustion chamber 9 can be fully utilized for efficient combustion.

(Effect of the device) As described above, according to the present invention, it is called on both sides directly below the nozzle.
In the area where the jet from the swirl chamber is difficult to flow, the jet is diffused through the lateral cavity, and the swirl flow in the large cavity is strengthened to increase the air utilization rate throughout the main combustion chamber. Therefore, there is an effect that the amount of unburned fuel during low load operation and the amount of smoke discharged during high load operation are significantly reduced.

[Brief description of drawings]

FIG. 1A is a longitudinal sectional view of an essential part of an embodiment of the present invention, and FIG. 1B is a plan view of its piston. FIG. 2A is a longitudinal sectional view of an essential part of another embodiment of the present invention, and FIG. 2B is a plan view of the piston. FIG. 3A is a longitudinal sectional view of a main part of a conventional example, and FIG. 3B is a plan view of the piston. 3 ... Piston, 4 ... Cylinder head, 5 ... Vortex chamber, 6 ... Injection port, 8 ... Piston top surface, 9 ... Main combustion chamber, 11,21 ... Trench part, 11e, 21e ... Trench Part bottom, 12 …… Large cavity, 12e …… Large cavity bottom, 15,25 …… Distributor, 14,24 …… Side cavity, 14
e, 24e …… Bottom of the side cavity, 14a, 24a …… Steps.

Claims (1)

[Scope of utility model registration request] 1. A combustion chamber of a swirl chamber type diesel engine in which an injection port from the swirl chamber is opened near the edge of the main combustion chamber,
On the top surface of the piston, there are formed left and right large cavity portions that spread out in a substantially circular shape from the region near the center of the piston, and left and right side cavity portions that branch from the trench portion below the injection port and communicate with each of the large cavity portions. , The depth of the lateral cavity portion is larger than that of the large cavity portion and smaller than that of the trench portion, and as an outer contour that defines the lateral cavity portion, with respect to the outer contour of the large cavity portion adjacent to the lateral cavity portion. A guide portion facing the tangential direction and having its end portion joined to the outer contour of the large cavity portion is raised from the bottom surface of the side cavity portion and is located between the left and right side cavity portions and faces the side cavity portion. A combustion chamber of a swirl chamber type diesel engine, characterized in that a dispersion table having a shape whose outer shape is substantially corresponding to the guide portion is raised.