JPH085305Y2 - Vortex chamber type diesel engine combustion chamber - 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) As a main combustion chamber shape of a swirl chamber type diesel engine,
The ones shown in FIGS. A and B are known. Explaining this, the cylinder head 4 has a pair of intake and exhaust ports 15,1.
6, and intake and exhaust valves 11 and 12 for opening and closing them, respectively, and the valve diameter of the intake valve 11 is formed to be larger than the exhaust valve 12 at a predetermined ratio, thereby achieving both the intake charging efficiency and the exhaust gas scavenging effect. It is like this.

A swirl chamber 5 provided in the cylinder head 4 so as to be positioned offset from the center of the cylinder communicates with the main combustion chamber 9 through an injection hole 6, and the top surface 8 of the piston 3 has the injection hole 6 A groove-shaped trench portion 7 extending in a radial direction along the piston center line O from a region substantially immediately below the main combustion chamber side opening portion.
And a substantially circular cavity portion 10 that extends from the region near the center of the end piston of the trench portion 7 to both sides, and these constitute a so-called clover leaf type cavity.

The valve seats 13, 14 are provided on the lower surface 4a of the cylinder head 4.
The circular recesses 17 and 18 are opened concentrically with a predetermined depth, and face the cavity portions 10 to define a disk-shaped space. A counterbore 19 is provided between the valve seats 13 and 14.
Is formed to prevent cracking of this portion due to heat during engine operation.

In this swirl chamber type combustion chamber structure, air flowing from the main combustion chamber 9 to the swirl chamber 5 through the injection hole 6 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 pass through the injection holes 6. Is ejected into the main combustion chamber 9. The fuel in this jetted gas is guided toward the center of the main combustion chamber 9 along the trench portion 7 of the piston 3,
Further, as shown by arrows a and b in FIG. 2A, a swirling flow is diffused into the disk-shaped space defined by the cavity portion 10 on both sides and the recesses 17 and 18 of the cylinder head 4, and the main combustion occurs. It will be mixed with room air and burned.

As a known example of this type of combustion chamber structure,
For example, there is Japanese Utility Model Publication No. 57-78724.

(Problems to be solved by the invention) However, in such a conventional swirl chamber combustion chamber, the recesses 17 and 18 formed in the lower surface 4a of the cylinder head 4 are provided in the intake and exhaust valves 11 and 12, respectively. Correspondingly, it is formed asymmetrically, and the intake side recess 17 overlaps with the trench portion 7, whereas the exhaust side recess 18 does not overlap with the trench portion 7, so that the cavity portion 10 and the trench portion 7 side The momentum of the jet flow that diffuses toward the intake side recess 17 is relatively large, and the cavity 10 where the exhaust valve side recess 18 faces is insufficiently mixed with fuel and air, and the air utilization rate is small. It tends to be. This causes an increase in the concentration of unburned fuel components in the exhaust during low load operation and an increase in the smoke concentration during high load operation.

The present invention aims to solve these conventional problems.

(Means for Solving the Problems) In order to achieve the above-mentioned object, in the present invention, a main combustion chamber formed between a cylinder head lower surface and a piston top surface,
The main combustion chamber is provided with an auxiliary chamber formed inside the cylinder head, and is opened near the edge of the main combustion chamber. In a combustion chamber of a swirl chamber type diesel engine in which a pair of intake ports and exhaust ports corresponding to intake valves and exhaust valves of different sizes arranged in a direction substantially orthogonal to the center line of the hole are opened on the lower surface of the cylinder head. On the top surface of the piston, there is a groove-shaped trench that extends from below the injection hole to near the center of the piston, and two substantially circular cavities that are continuous near the center of the piston in this trench and that symmetrically expand across the trench. On the other hand, the lower surface of the cylinder head surrounds the intake valve and the exhaust valve, and a part of each of them overlaps with the piston center of the trench part. To form two circular recesses of identical diameter which are arranged symmetrically with respect to switch unit.

(Operation) In the above-mentioned configuration, the jet of the combustion gas containing the fuel ejected from the swirl chamber to the main combustion chamber through the injection hole first hits the groove-shaped trench portion formed along the jet center, and from this trench portion The flow splits and diffuses as a swirling flow into two disk-shaped spaces defined between each cavity on the top surface of the piston and each recess on the bottom surface of the cylinder head. Since they are polymerized and formed so as to be symmetrical with respect to the center of the jet, the jets are split almost evenly with respect to the jetting direction of the jet and diffuse into the main combustion chamber. Therefore, the jet of the combustion gas containing the fuel is sufficiently diffused over a wide range of the main combustion chamber, and good combustion properties are obtained.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. The parts corresponding to those in FIGS. 2A and 2B are designated by the same reference numerals.

A swirl chamber 5 and an injection hole 6 are formed in the cylinder head 4 near the edge of the main combustion chamber 9, and a groove-shaped trench portion 7 extending from the region directly below the injection hole 6 to the center of the piston is formed in the piston 3. A substantially circular cavity portion 10 formed on the O and extending from the end region (center of the piston) of the trench portion 7 to both sides is formed, and these constitute a so-called clover leaf type cavity.

A pair of intake / exhaust ports 15,1 on the lower surface 4a of the cylinder head 4.
6 and the intake / exhaust valves 11 and 12 are arranged so as to sandwich the center line O. The valve diameter of the intake valve 11 is formed larger than that of the exhaust valve 12 at a predetermined ratio.

On the lower surface 4a of the cylinder head 4, a circular recell 21 is formed concentrically with the intake / exhaust port 15, and the intake valve 11 is provided with a valve seat 13
The face end surface 11a and the recess 21 in the state of being seated on the head lower surface 4a define a circular recess having a predetermined depth.

A circular recess 22 is formed on the lower surface 4a of the cylinder head 4 so as to be eccentric to the exhaust port 16 and surround the exhaust port 16, and the recess 22 is formed.
A circular recess 23 is formed inside the member 22 concentrically with the exhaust port 16. With the exhaust valve 12 seated on the valve seat 14, the face end surface 12a and the recessed step portion 22a and the inner peripheral portion 22b of the recess 22 define a circular recess having the same depth as the recess 21 with respect to the head lower surface 4a. It is supposed to do.

The intake-side recess 21 and the exhaust-side recess 22 have substantially the same diameter as the cavity portion 10, and each cavity portion 10
The piston center line O so as to face each other. When the piston 3 is near the top dead center, each recess 2 is formed.
Two disk-shaped spaces are defined between 1, 22 and each cavity 10.

The intake-side recess 21 and the exhaust-side recess 22 are arranged so as to intersect with each other on the piston center line O, and are overlapped with the groove-shaped trench portion 7 of the piston 3 in plan projection at the same ratio.

The stepped portion 22a of the recess 22 is provided with a countersunk portion 25 located between the valve seats 13 and 14 to prevent the portion from cracking due to heat during engine operation.

It is configured in this way, and the operation will be described next.

The jet of combustion gas containing fuel, which is jetted from the swirl chamber 5 to the main combustion chamber 9 through the nozzle holes 6, first hits a groove-shaped trench portion 7 formed along the jet center, and from this trench portion 7 As shown by arrows c and d in FIG. A, the flow is divided into swirling flows and diffused into each disk-shaped space defined between each cavity 10 of the piston 3 and each recess 21, 22 on the lower surface 4a of the cylinder head. To do.

At this time, by forming the recess 22 eccentrically with respect to the small-diameter exhaust valve 12, the two disk-shaped spaces are symmetrically formed with respect to the center of the jet flow, and the recesses 21, 2 are formed.
Since 2 is superposed on the trench portion 7 together with each cavity portion 10, the jet flow is split from the trench portion 7 substantially evenly in the directions of arrows c and d, and is diffused symmetrically in the main combustion chamber 9. go. Therefore, the jet flow of the combustion gas containing the fuel is sufficiently diffused over a wide range of the main combustion chamber 9, and the air in the main combustion chamber 9 is effectively used to obtain good combustion properties.

(Effect of the Invention) As described above, according to the present invention, the intake valve and the exhaust valve having different sizes are arranged so as to be substantially orthogonal to the center line of the injection hole of the swirl chamber, and the groove shape of the piston top surface is arranged. In a combustion chamber having a structure in which two cavity portions extending from a trench portion in a clover leaf shape are formed so as to face the intake and exhaust valves,
A circular recess that surrounds a pair of intake and exhaust valves is formed on the lower surface of the cylinder head and is formed to have the same diameter as that of the trench. The jet ejected from the swirl chamber is defined by each recess and each cavity from the trench. Since it is divided equally into two disk-shaped spaces and symmetrically diffused into the main combustion chamber, the air utilization rate can be increased over the entire area of the main combustion chamber, and therefore the unburned fuel content and high load during low load operation can be increased. This produces an effect that the amount of smoke emitted during operation is significantly reduced.

[Brief description of drawings]

1A is a plan view of a cylinder head according to an embodiment of the present invention, and FIG. 1B is a side sectional view taken along line XX of FIG.
FIG. 2A is a plan view of a cylinder head showing a conventional example,
FIG. B is a side sectional view taken along line XX of FIG. 3 ... Piston, 4 ... Cylinder head, 4a ... Head bottom surface,
5 ... Vortex chamber, 6 ... Injection hole, 7 ... Trench part, 9 ... Main combustion chamber, 10 ... Cavity part, 11 ... Intake valve, 12 ... Exhaust valve, 21,2
2 ... recess

Claims (1)

[Scope of utility model registration request] 1. A main combustion chamber formed between a lower surface of a cylinder head and a top surface of a piston, and a sub chamber formed inside a cylinder head, the opening being near an edge of the main combustion chamber, and , The main combustion chamber and the auxiliary chamber communicate with each other through the injection hole directed toward the center of the piston, and the intake valve and the exhaust valve, which are arranged in the direction substantially orthogonal to the center line of the injection hole, have different sizes. In a combustion chamber of a swirl chamber type diesel engine in which a pair of intake ports and exhaust ports are opened on the lower surface of the cylinder head, a groove-like trench portion extending from below the injection hole to near the center of the piston is formed on the top surface of the piston. , Which forms two circular cavities that are continuous in the vicinity of the piston center and that extend symmetrically across the trench, while enclosing the intake valve and exhaust valve on the lower surface of the cylinder head. Combustion of a swirl chamber type diesel engine, characterized in that a part of each of them overlaps near the center of the piston in the trench part and further forms two circular recesses of the same diameter symmetrically arranged with respect to the trench part. Room.