JP2797811B2 - 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 a combustion chamber of a swirl chamber type diesel engine in which a jet flows from a swirl chamber formed in a cylinder head to a main combustion chamber between a cylinder head and a piston.

[0002]

2. Description of the Related Art In a diesel engine having a configuration in which a vortex chamber formed in a cylinder head communicates with a main combustion chamber formed between a cylinder head and a piston, FIG. , And FIG. 5A
Some have a combustion chamber structure as shown in FIG. 6, which is a cross-sectional view including a cylinder block and a piston along the line A (see Japanese Utility Model Laid-Open No. 1-105724). Piston 3 and cylinder head 5 housed in cylinder block 1
A main combustion chamber 7 is formed between the piston and the cylinder head 5, and a swirl chamber 9 is formed in the cylinder head 5 at a position eccentric from the center of the piston 3. The main combustion chamber 7 and the vortex chamber 9 are formed by the main combustion chamber 7
Are communicated with each other through an injection hole 11 near the outer peripheral edge of the nozzle.

On the top surface of the piston 3, a groove-shaped trench portion 13 extending from the vicinity of the injection hole 11 of the cylinder head 5 toward the center of the piston 3 along the piston center line S, A pair of substantially circular cavities 15 and 17 are formed to extend to the left and right sides of the pair 13, respectively, and form a so-called cloverleaf-type cavity.

On the other hand, a pair of intake / exhaust ports 19 and 21 are formed in the cylinder head 5 and open to the main combustion chamber 7 so as to sandwich the piston center line S.
9 ・ 21 are intake / exhaust valves 2 mounted on the cylinder head 5
It is opened and closed by 3.25. The valve diameter of the intake valve 23 is formed to be larger than the valve diameter of the exhaust valve 25 at a predetermined ratio, so that the intake charging efficiency and the exhaust gas scavenging effect are compatible.

A circular recess 27 is formed concentrically with the intake port 19 around the opening of the intake port 19 on the lower surface of the cylinder head 5. When the intake valve 23 is seated on the valve seat 29, the face end face 23a and the recess 27 define a circular concave portion having a predetermined depth with respect to the head lower surface 5a.

A circular outer recess 31 eccentric to the exhaust port 21 is formed on the lower surface of the cylinder head 5 around the exhaust port 21, and an inner circular recess concentric with the exhaust port 21 is formed inside the circular outer recess 31. 33 are formed. When the exhaust valve 25 is seated on the valve seat 35, the face end face 25a, the recess step 31a and the side wall 31b of the recess 31 define a circular recess having the same depth as the recess 27 with respect to the head lower surface 5a. It has become.

The recess 27 on the intake side and the recess 3 on the exhaust side
Each of the cavities 15 and 1 has substantially the same diameter as the cavities 15 and 17 on the piston 3 side.
7 is provided symmetrically with respect to the center line S of the piston 3 so as to oppose the center line S. When the piston 3 is near the top dead center, two disc-shaped portions are formed between the recesses 27 and 31 and the cavities 15 and 17. A space is defined. Also, the recess 27 on the intake side
The exhaust-side recesses 31 are disposed so as to intersect with each other on the piston center line S, and are overlapped with the trench portions 13 of the piston 3 at the same ratio in plan projection.

A counterbore 37 is formed between the valve seats 29 and 35 in the step 31a of the exhaust-side recess 31. The formation of the counterbore 37 prevents generation of cracks due to heat during operation of the engine.

In such a swirl chamber type diesel engine,
The air during the compression stroke flows into the swirl chamber 9 through the injection hole 11, thereby generating a strong swirl. The fuel is injected into the swirl to achieve sufficient mixing and combustion. Vortex chamber 9 to injection hole 11
First, the jet of the combustion gas containing fuel ejected to the main combustion chamber 7 through the trench 1 is formed along the center of the jet.
5, the air flows from the trench 13 to the left and right as shown by arrows B and C in FIG.
Recesses 5, 17 and lower surface 5 a of cylinder head 5
7 and 31, and is diffused as a swirling flow in each of the disk-shaped spaces defined between them.

At this time, the recess 31 on the side of the exhaust valve 25 having a small diameter with respect to the intake valve 23 is formed eccentrically with respect to the exhaust valve 25, so that the two disk-shaped spaces become symmetric with respect to the center of the jet. In addition, since the recesses 27 and 31 are superimposed on the trench 13 together with the cavities 15 and 17, the jet flowing out into the main combustion chamber 7 is equally divided and diffused into the left and right disk-shaped spaces, and the main combustion is performed. The air in the chamber 7 is effectively used, and the combustion is improved.

[0011]

As means for further improving the combustion mode, it is known to increase the compression ratio by reducing the volume of the main combustion chamber 7 or to increase the volume ratio of the vortex chamber 9. Have been. Increasing the compression ratio shortens the ignition delay period and reduces HC, so that the injection timing can be delayed and NOx decreases. On the other hand, when the volume ratio of the swirl chamber 9 is increased, HC and smoke are reduced and output is improved, but NOx is increased. For this reason, if the compression ratio is increased and the volume ratio of the vortex chamber 9 is increased at the same time, the emission of HC, SOF (soluble organic substances), smoke, etc. can be reduced without increasing NOx, and the output can be reduced. Improvement can be achieved.

In order to realize this, the cavity 1
It is effective to reduce the volume of the main combustion chamber 7 by reducing the volume of 5, 17.

However, when the area of the cavities 15 and 17 is simply reduced or the depth thereof is reduced to reduce the volume of the cavities 15 and 17, the cavities flow out of the swirl chamber 9 into the main combustion chamber 7. The diffusion velocity component of the jet relatively increases, and the jet flows into the cavity 1 at the outer peripheral edge of the piston 3.
5 and 17 and the recesses 27 and 31 collides with the inner wall of the cylinder, and the portion to be extinguished increases. As a result, in the main combustion chamber 7, there is a problem that the air utilization rate is reduced and the combustion form cannot be further improved as a whole.

Accordingly, an object of the present invention is to further improve the combustion mode without lowering the air utilization rate in the main combustion chamber.

[0015]

In order to achieve the above object, the present invention provides a cylinder head having a pair of intake / exhaust ports opening to a main combustion chamber formed between the cylinder head and a piston, and Vortex chambers communicating with each other near the outer peripheral edge of the combustion chamber are provided, and around the opening of the suction / exhaust port to the main combustion chamber, symmetrical with respect to the center of the jet flowing out from the vortex chamber to the main combustion chamber. And circular recesses whose outer peripheral edges are close to each other are formed, and a notch is formed in the vicinity of each of the circular recesses so that the circular recesses communicate with each other. The side wall of the notch facing the jet flow has a curved surface. While forming
A trench formed on the top surface of the piston includes a guide groove that guides the jet from the vortex chamber and extends near the center of the piston, and an arc-shaped branch groove that is continuous with the guide groove and formed concentrically with the circular recess. The trench portion is configured such that the outer peripheral edge of each branch groove is located inside the outer peripheral edge of the circular concave portion.

[0016]

In the combustion chamber of the vortex chamber type diesel engine having such a configuration, the jet from the vortex chamber flows out into a trench formed on the top surface of the piston and is guided by the guide groove near the center of the piston. Are equally divided into the left and right branch grooves, and are swirled and diffused into two disk-shaped spaces between the circular recess formed on the lower surface of the cylinder head. At this time, since the outer peripheral edge of the branch groove of the trench portion is located inside the outer peripheral edge of the circular concave portion on the lower surface of the cylinder head, most of the jet flow guided to the trench portion flows into the circular concave portion and climbs over the circular concave portion. The components that reach the inner wall and extinguish are reduced, and good combustion properties are obtained. Also, the trench part
Since it is formed by the linear guide groove and the two arc-shaped branch grooves, the volume of the main combustion chamber is reduced as compared with a conventional so-called cloverleaf-type cavity,
As a result, an increase in the compression ratio and an increase in the volume ratio of the vortex chamber are realized at the same time, and H2 is increased without increasing NOx.
The emission of C and the like is reduced, and the output is improved. In addition, 2
A notch is formed at a position adjacent to the two circular recesses, and the side wall of the notch facing the jet flow has a curved shape. The occurrence is prevented.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view from the top of a piston of a diesel engine, and FIG. 2 is a sectional view including a cylinder head and a cylinder block taken along line DD of FIG. A main combustion chamber 45 is formed between the piston 41 housed in the cylinder block 39 and the cylinder head 43.
On the other hand, a swirl chamber 47 is formed in the cylinder head 43 at a position eccentric from the center of the piston 41. The main combustion chamber 45 and the vortex chamber 47 communicate with each other through an injection hole 49 near the outer peripheral edge of the main combustion chamber 45.

Intake valve 5 provided on cylinder head 43
An intake-side recess 55 as a circular recess similar to that of the conventional example shown in FIGS. 5 and 6 is formed around the opening of the intake port 53 that opens and closes on the main combustion chamber 45 side. . In addition, around the opening of the main combustion chamber 45 side of the unillustrated exhaust port in which the exhaust valve 56 opens and closes, an inner recess concentric with the exhaust port, similar to the conventional example shown in FIGS. In addition, an exhaust-side recess 57 is formed as a circular recess eccentric to the exhaust port outside the inner recess.

Each of these recesses 55 and 57 has a piston 4
It is located at a position slightly shifted from the center line P to the side opposite to the injection hole 49, and the center line is indicated by Q. The recesses 55 and 57 are connected to each other by a communication portion 5 as a notch.
The side wall 61 on the side facing the jet from the injection hole 49 of the swirl chamber 47 in the communication part 59 has a curved surface shape.

On the top surface of the piston 41, a guide groove 63 extending from near the outer peripheral edge of the piston 41 facing the injection hole 49 on the cylinder head 43 side to near the center of the piston 41,
A trench portion 69 is provided which includes branch grooves 65 and 67 which are symmetrically branched from the guide groove 63 toward the left and right recesses 55 and 57 near the center of the piston 41. Each of the branch grooves 65 and 67 is formed in an arc shape and has a recess 5.
5 and 57 are arranged in a region of about 1/3 of the entire circumference.
The outer peripheral edges 65a, 67a of the
7 is located inside the outer peripheral edge. Each branch groove 65,
The boundary portion 71 between the 67 has a curved shape like the side wall 61 of the communicating portion 59 between the recesses 55 and 57.

In the combustion chamber of the vortex chamber type diesel engine having such a configuration, when the jet of the combustion gas containing the fuel in the vortex chamber 47 flows into the guide groove 63 of the trench portion 69 through the injection hole 49, This jet flows toward the vicinity of the center of the piston 41 while being guided by the guide groove 63, and is equally divided into left and right branch grooves 65 and 67 provided symmetrically as shown by arrows F and G.

The outer peripheral edges 65a, 67a of the branch grooves 65, 67 of the trench portion 69 are located inside the outer peripheral edges of the recesses 55, 57.
Most of the jet flowing toward 5, 67 flows into each of the recesses 55, 57 and flows into each of the recesses 55, 57 as shown by the solid arrows in FIG. Instead, the amount of the jet flowing toward the inner wall of the cylinder is small.
Therefore, a large amount of jet flowing into each of the recesses 55 and 57 generates a strong swirling flow centered on each of the recesses 55 and 57, and
Components that reach the cylinder inner wall and extinguish are reduced, and the air in the main combustion chamber 45 is effectively used to obtain good combustion properties. In FIG. 3, the dashed line is the outer peripheral portion of the cavity of the conventional example, and the flow of the jet indicated by the arrow of the dashed line is that of the conventional example.

Since the trench 69 formed on the top surface of the piston 41 is formed by the linear guide groove 63 and the two arc-shaped branch grooves 65 and 67, the main combustion chamber 4 is formed.
5 is smaller than that of a conventional so-called cloverleaf-type cavity, thereby simultaneously increasing the compression ratio and increasing the volume ratio of the swirl chamber 47, and increasing NOx. The emission of HC, SOF, smoke and the like is reduced, and the output is improved. Furthermore, the side wall 61 in the communication portion 59 between the two recesses 55 and 57 and the boundary portion 7 between the branch grooves 65 and 67.
Since each of the nozzles 1 has a curved surface shape, even if the jet from the injection hole 49 of the swirl chamber 47 is blown toward the side wall 61 and the vicinity of the boundary portion 71, these portions are not broken by heat.

FIG. 4 shows another embodiment of the present invention. In this embodiment, a slope portion 65 is provided at each end portion of the two branch grooves 65 and 67 so as to gradually rise toward the top surface of the piston 41 with respect to the bottom surface of the branch grooves 65 and 67.
b, 67b. In this case, the branch grooves 65, 67
Is smoothly guided toward the recesses 55 and 57 by the slope portions 65b and 67b without stagnation, and a stronger swirling flow is generated. Therefore, the air utilization rate in the main combustion chamber 45 is further improved.

[0026]

As described above, according to the present invention, the outer peripheral edge of the branch groove of the trench formed on the top surface of the piston is located inside the outer peripheral edge of the circular concave portion on the lower surface of the cylinder head. Therefore, most of the jet flow guided to the trench portion flows into the circular concave portion, passes over the circular concave portion, reaches the inner wall of the cylinder, reduces the amount of flame-extinguishing components, improves the air utilization rate in the main combustion chamber, and improves the efficiency. Combustion properties can be obtained. The trench portion has a linear guide groove and an arc-shaped two groove.
Since the main combustion chamber is formed by two branch grooves, the volume of the main combustion chamber is reduced as compared with the conventional so-called cloverleaf type cavity, thereby increasing the compression ratio and reducing the volume ratio of the vortex chamber. Expansion can be realized at the same time, NO
It becomes possible to reduce the emission amount of HC and the like without increasing x, and the output is improved. Furthermore, since the side wall on the side facing the jet from the vortex chamber has a curved shape in the cutout portion of the two circular concave portions adjacent to each other,
The generation of cracks near the side wall due to the heat of the jet can be prevented.

[Brief description of the drawings]

FIG. 1 is a top view of a piston including a positional relationship between a recess on a cylinder head side and a swirl chamber, showing one embodiment of the present invention.

FIG. 2 is a sectional view including a cylinder head and a cylinder block taken along line DD of FIG. 1;

FIG. 3 is an enlarged cross-sectional view including a cylinder head taken along line EE of FIG. 1;

FIG. 4 is a top view of a piston including a cylinder head side recess and a positional relationship with a swirl chamber, showing another embodiment of the present invention.

FIG. 5 is a bottom view of a cylinder head including a positional relationship with a trench on the piston side, showing a conventional example.

FIG. 6 is a sectional view including a piston and a cylinder block taken along line AA of FIG. 5;

[Explanation of symbols]

 41 Piston 43 Cylinder Head 45 Main Combustion Chamber 47 Eddy Flow Chamber 51 Intake Valve 53 Intake Port 55, 57 Recess (Circular Recess) 63 Guide Groove 65, 67 Branch Groove 69 Trench 59 Communication Portion (Notch) 61 Side Wall

Claims (1)

(57) [Claims] A cylinder head is provided with a pair of intake / exhaust ports opening to a main combustion chamber formed between a cylinder head and a piston, and a vortex chamber communicating with a portion near an outer peripheral edge of the main combustion chamber. Around the opening of the intake / exhaust port to the main combustion chamber, a circular recess is formed symmetrically with respect to the center of the jet flowing out from the vortex chamber to the main combustion chamber and the outer peripheral edges of which are close to each other. A notch portion in which the circular concave portions communicate with each other is provided in the vicinity of each circular concave portion, and the side wall of the notch portion facing the jet flow is formed in a curved shape,
A trench formed on the top surface of the piston includes a guide groove that guides the jet from the vortex chamber and extends near the center of the piston, and an arc-shaped branch groove that is continuous with the guide groove and formed concentrically with the circular recess. A combustion chamber of a vortex chamber type diesel engine, wherein an outer peripheral edge of each of the branch grooves is located inside an outer peripheral edge of the circular recess.